Discussing WHAT you should write down when answering exam questions is extremely useful to GCSE and A-level pupils. This video should be played in school Maths lessons. Thank-you so much.
To get top grade (grade 9) on AQA 2019 you needed to average around 86% across 3 exams that included this one. Both Tom and Ben got above 90% so were on course for a 9 :)
My tutor gave me what was, for me at least, amazing advice when tackling exam papers. First thing you do, when the timer starts, put down all your stationery, and read through the paper. You will see many questions where you know you have the knowledge to at least tackle them, and also to do those ones first. If the first few questions happen to be ones that trip you up, you can get into a really anxious state so easily, when the rest of the paper may be fine for you. Going through the ones you're confident with first helps you settle so much better. Really helped me with my anxiety for exams :)
To anyone taking a real exam and tends to refine their graphs by drawing it in multiple strokes like Tom does: draw and refine it in pencil first, then trace the final line in pen and erase your pencil sketch. Even if you’re unable to completely erase it, the single pen line removes any ambiguity about which exact line you consider to be your final answer, and that ambiguity is the biggest reason they deduct points for feathering.
@@wesleyml3682 Then use a heavy pencil stroke for the final line and erase the initial light strokes as best as you can. In any case, do your best to make it unambiguous.
@@ragnkja Of course! That's what I'd do, for the times when there was any difficulty, of course. :) Thankfully those days are long gone and in university I only ever need to plot using R and Python.
It's pretty awe inspiring to see how a maths whizz brain works. Both you people are what I wished I was when doing O level maths all those years ago. Our young peoples maths progress is in good hands not just from your knowledge but your kindness and the way both of you are as human beings. Back in my day maths teachers instilled fear and were mostly grumpy, aggressive teachers that were only interested in the real high flyers of the class.
This is such a great video! I’m so glad I discovered your channel today, I know my students will find this kind of discussion incredibly useful! Keep up the fantastic content 😁🙏🏼
I totally agree. I dont use maths in my day to day job, but I do some at home out of passion. I had an absolute blast watching these videos and I'm sure that young students will too. The relaxed nature of the videos and seeing two teachers do what they will soon do in the future could be eye opening and motivating for them. Hope you'll have success with them
For the triangle and tangent problem, you could have also argued that the triangle can be cut down its symmetry line. That symmetry line is square to the remaining side AB. It's also a symmetry line of the circle, because it's a symmetric triangle in a circle = hits the center. So the same as the sqare line to the tangent in point C. AB is square to CO, CO is square to CD. = parallel.
Question 24 iand 27 are straight forward if you use the Unit circle. And please note that the graphes that you two drew, are derived FROM the unit circle! Now I'm just being a math teacher :) But hey, I LOVE this video! Please do more..
The unavoidable q20. The mark scheme also allows the dropping of the perpendicular from C to the midpoint of AB through the circle centre (it's an isosceles triangle) and that goes through the centre of the circumscribed circle (symmetry, but easy to prove if you are bored). So you have a right angle with AB and a right angle at CD, so internal angles add up to two right angles, so you have two parallel lines.
@@navidtawsif9609 You'll need a pencil and paper to follow this: sorry. If only I could post pictures. This is might not be the simplest way to show that the perpendicular from the apex of an isosceles triangle to the opposite side goes through the centre of the circumscribed circle, but here goes: Consider an isosceles triangle ABC, with AB = AC. Let the centre of the circumscribed circle be O, then OA = OB = OC because they are radii. Triangles AOB ≅ AOC by SSS (AO = AO (shared), AC = AB (isosceles Δ) and OB = OC (radii)). Therefore ∠BAO = ∠CAO = ∠ABO = ∠ACO because of the congruence and Δs ABO and ACO are also isosceles (radii of the circumscribed circle). Let ∠BAO = α then ∠AOB = ∠AOC = (π - 2α) Draw OM perpendicular to BC where M is on BC. OB = OC (radii), so ∠OBM = ∠OCM. ∠OMB = ∠OMC = 90° by construction. Therefore ∠BOM = ∠COM = (90° - ∠OBM). Now, ∠BOC = 2π - 2(π - 2α) = 4α. ∠BOM = ∠ COM = 2α. ∠AOB + ∠BOM = (π - 2α) + 2α = π therefore AOM is a straight line and AM is the perpendicular from A to BC that goes through O, the centre of the circumscribed circle. QED. Edit: it might be quicker to assume the theorem that says the angle subtended by a chord at the centre of a circle is twice that subtended at the circumference. That gives you ∠BOC = 2∠BAC and then you draw OM and go from there. To prove that theorem, you basically do what I did above, so they are equivalent and my proof doesn't assume the angle at centre theorem.
What a brilliant video. Fantastic chemistry between you both, and super useful for students (or their teachers) in providing insights into the marking schemes used behind the scenes and therefore what is important. Well done do you both.
This is an amazing Maths conversation. Regarding Question 20. If you remove the Isoceles condition that AC=BC. Then the Chord formed by AB can go through a whole variety of angles to the tangent CD. If for instance AC is tiny and BC is maximised then the angle will be almost 90 degrees. Likewise is BC is tiny and AC is maximised it will be -90 degrees. If you imagine a whole series of possibilities for the chord AB it will form a continuum between +90 degrees and -90 degrees according to the different lengths of AC and BC. Halfway between these two possibilities (+90 degrees and -90 degrees) there must be some combination of lengths of AC and BC where then angle between the tangent CD and the Chord AB is zero (ie they are parallel) It makes sense for this to be halfway along the diffferent possibiilties for the lengths of AC and BC when they are equal. This seems intuitive reasoning to me but I am not sure whether this would be a good enough proof to get the marks in this question.
I find it so intresting as just went on a trip with my class and ended up seeing him give a talk, then I realised I already knew him from youtube. Loved the talk about how maths can save the environments keep up the good work.
Sorry about the excessive comments below. This was amazingly interesting. Blimey! Teachers marking these papers have a real job on their hands (I read the marking scheme because, well, OCD, probably). And the pupils taking these papers seem to have to learn an "exam language" where some keywords give a clue about what you need to do and in how much detail. I don't remember that from 40+ years ago when I was doing O levels (probably my age). I'll go now: I promise.
Great non-competitive math test video 👏👏 I just want to say that the last question is much easier than what you both thought: Cos(x)= sin(60) x [sin(30)/cos(30)] >> cos(x) cos(30)= sin(60) sin(30). >> x= 60. {because cos(y)= sin(90-y)}
@@asamet2007 Did you read my other comment I posted? I say the exact same thing. I even go into further detail explaining how cos(x)=sin(53) x tan(37) couldn't be solved the way they did it, but can clearly be solved this way. The problem is that the marking guide doesn't allow for it. M1 in the marking guide basically says you have to come up with values for sin(60) or tan(30) or cos(30) and sin(30). You have to come up with the actual values. M2 says once you have those values you have to use the values to find x. Writing down cos(x)=1/2 is enough to get the points on M2. But writing down cos(x)=cos(60) isn't. You can't get points on M2 without getting points for M1 it's "M1dep" Then to get points for A1 you have to write down 60 AND get points for M2. Don't believe me? Check out the marking guide: tomrocksmaths.files.wordpress.com/2021/10/aqa-83001h-w-ms-jun19.pdf So no points for you or me. 😞
It's weird watching this now knowing I had sat this exam 3 years ago, doing it now and seeing the little mistakes I had done back then recorrected by myself. Great video series otherwise for people doing either gcse or a level maths seeing someone higher doing it
For cos(x) = sin(60).tan(30), you can solve by remembering tan = sin/cos and sin(90-x) = cos(x). sin(60).tan(30) = sin(60).sin(30)/cos(30) = sin(60).cos(60)/sin(60) = cos(60). Therefore x = 60, even if you don't know the values for sin and cos at those angles.
55:40(ish) Ben is correctly explaining the Alternate Segment Theorem: ACD = ABC. I'm pretty sure that, in his "doing the exam" video, he said ACD = BAC (which is, in general, wrong) and was worried about not having used the isosceles property of triangle ABC. That last fact is what makes ACD = BAC. My suspicion is that Tom should not have awarded full marks here (Tom admits to not having followed the geometry - give the guy some slack: he's a brilliant mathematician but not a geometer). Perhaps I need to keep watching... (bad habit of commenting before the video ends) Having worked through the mark scheme, I am so, so glad that I don't have to mark these papers. Am totally loving this series of videos!! (Note to self: look out the A level ones).
It was great to see that the paper they did was exactly identical to the mock I had today 💀🤣. Yes they should do another, perhaps I’ll get lucky again 🤣
I remember an exam where first part was limits and second part was derivatives. Because the time was generous and I kinda knew I get trough the exam with spare time I decided to work it little differently. I first proved Hopital's method and used it to solve the limits. I got F from that part.
I never thought I would like maths again after A-level and then Software engineering at uni but its kind of like car crash watching... I cant stop lol. Kudos Dr!
A question I’d love to see you solve is to find ‘r’ (sometimes written as ‘i’) in an annuity formula. I once tried to make each letter the subject in the formula, but got stuck with ‘r’, which appears twice, before being told by someone it cannot be done. I saw a video where a ‘brute force’ method was used to get an approximation of ‘r’, but I was quite confused as to what was going on. Yet it still baffles me why ‘r’ cannot be made the subject using factorisation and knowledge of algebra. The formula looks like this: A = P [(1+r)n -1/r] where n is a power. Pls consider solving this in a future video. By the way, really enjoy your videos and have learned a great deal from watching them.
Quadrilateral has 360 degrees because you can always divide it into two triangles. Quite a surprize that you could not figuer this out .. But I love the openess!
I definitely want to see you both attempt a Senior Math Challenge or BMO Round 1 exam! I think it'll be an interesting "not competition" if you don't immediately know how to solve every question haha
The more advanced the questions the exams get, the easier it becomes for him to solve it. The only difficulty is him trying to remember basic maths equations to figure them out.
@38:00 A quick way to calculate the sum internal angles of any polygon is (n-2) * 180. Where n is the number of angles. Also for 3D geometry, F + V = E + 2, where F is the number of faces, V (vertices) and E (edges)
In Q20 I didn't use that fancy theorem, I drew the perpendiular from C to the centre, so we have that the angle we care (the one equal to x and therefore the two lines are parallel) + another angle (let's call it y) is 90 deg. Now y is an angle on the base of an isoceles tirangle with "big" angle 2x (it insits on the same point as the startign triangle and therefore is the double). So y=(180-2x)/2=90-x but then 90=y + angle we care=90-x+angle we care=> angle we care=x
Re: sum of internal angles I always imagine something I was shown as a kid where you just add a triangle to an existing shape such that a side matches and all the internal angles would still add up for the new shape and since you replaces one side with 2 it's a net change of +1 side. Triangle + triangle = square, so must be 180°+180° = 360° Square + triangle = pentagon, so a pentagon must be 360°+180°=540° Etc.
would love to see you attempt the A level Math paper from Singapore, especially the H2 and H3 levels... really want to hear your opinion on these papers especially given that they are set by the same cambridge authority as the international/uk A level and yet they are so so different from each other!
That was great fun, thank you both for taking the time to do that. Based on the tutoring that I have done, I think that's really useful for GCSE maths students to watch. (I couldn't agree more about the circle theorems, I hate the GCSE syllabus for doing this, what is it trying to achieve?)
Ben, I totally agree with you on mixed integers and ratiometric fractions! They are as obsolete as Roman numerals. By all means leave ratios unsimplified to preserve accuracy during calculations, but there's no reason to describe something like 5/2 as anything besides 5/2 or 2.5. All real-life measuring instruments -- rulers, voltmeters, weighing scales ..... --- read decimal fractions anyway ..... #RealLifeIsDecimal Also, "engineering notation" is a special form of exponential notation where the exponent is always a multiple of 3 so as to line up with a measurement prefix. For example, 589 * 10 ** -3 as opposed to 5.89 * 10 ** -7.
i remember when i learned about sin, cos, and tan we neither had those triangles nor any graphs. my teacher just gave us a paper and said "here are some important to know numbers for sin and cos. learn them" .... i don´t have to explain i already forgot those exact numbers, the only thing i remembered was "yeah sin60 was one of those numbers i had to learn"
Feathering penalty should be for students trying to sneak an obviously wrong answer through by having different lines go through different points and appear to be one graph. Here it was very clear what the intended line was. Harsh marking was harsh.
My faith in humanity has been restored. Nerds worldwide should do this stuff from AI/Machine Learning to Programming, Medicine, Quantum Computing, Law and Aircraft Technology.
For Q10, without marking/scoring guidance I had penalized Ben because he drew the curve all the way through x=5 and missed the correct value of Y(5) by 2. I’m glad to see the guidance is precise enough that it clearly states that this must be ignored.
Standard form is a number between 1 (inclusive) and LESS than BASE times a power of BASE. BASE in this case is 10. Floating point numbers (in computing) are the same format only the base is 2 and the power represents a shift value. (There's also a strange bias usually). The double line on the reciprocal graph (which I saw you making in the previous video) looked like an issue to me. Had you infilled it bold, you might have 'got away with it'. The simplify fully is a bit rough, but 4 and 6 do have a common factor... I somehow got to Comp Sci degree level without knowing the difference of squares identity, but I used the sum of squares identity months later in commercial programming to optimize multiply to 3 square look ups. I've been teaching my son some O-level maths and the alternate segment theorem cropped up. Again, news to me. It's said, you wouldn't ask Einstein to do a simple calculation, so the special case looks fine. Overall what strikes me most is that marking these things is way harder than doing them. I now have an appreciation that the marking system is remarkably fair. Nice video guys.
1:11:50-something. Tom asserts that he should have had the marks if he had differentiated (apparently not a GCSE thing - I have no idea, my maths O level (the then equivalent) was over 40 years ago). That reminds me of Mathologer (definitely a non-remunerated plug: subscribe to TRM and Mathologer and have multiple excuses to not do the washing up) who had, in uni, a proof rejected because it wasn't the one in the course (even though it was right).
Writing really good questions and allocating marks is a highly refined skill. Poorly written questions lead to poorly constructed mark schemes. 1 mark should be awarded per concept, calculation or demonstrated skill.
I love how both of you are complaining about GCSE "command words" the same way I am complaining about them in the German A-levels equivalent. Even worse, some of those are used in multiple subjects but mean slightly different things in each.
I would have awared the mark on the graph Q. I would look at it and think the students first line wasnt going through the points so he drew a second line and it wad clear you drew large crosses at the correct points to show the correct intend line. It is difficult to cross out graphs lines close together... definitely not gona penalise on that if I was an examiner
Hello Tom, it is fascinating to watch these kind of videos! I live in Hong Kong and we have Public exam call the HKDSE. You should try doing it :)))). There are many practice paper or past paper in the Internet :)))
i retook a maths paper higher the other day , ive been gone for 3 years now out of school and i still got a B which im shocked considering i forgot so much stuff
It's the sort of maths exam that Albert Einstein would fail. Imagine a top C++ programmer being asked to sit an exam on binary division calculated by hand or assemly language etc
30:17 here we go again...it says "the triangular CROSS SECTION of a prism", not "this is the whole prism". Hence the volume of the given triangular cross section is equal to 51cm^3.
I can't believe that you both still are complicating 20a) when it is dead obvious that a line from C to the midpoint of AB goes through the center of the circle and is therefore perpendicular to both AB and the tangent through C. (It does helps to draw the figure accurately).
Oh man do I have doosey of a video suggestion for you. -using Simpson’s method in order o find the centroid of an airfoil. -me and my senior design group were stumped for about 5 hours on it.
55:10 if you have an isosceles triangle inscribed in a circle, doesn't the line bisecting the triangle between the two equal-length sides necessarily pass through the centre of the circle? Which would make it perpendicular to the tangent line, and then the rest follows easily. Unless I've missed something here, it looks like the extremely wonky diagram they used has deliberately obfuscated what should be an intuitive fact
Wait really? I'm doing higher and I don't know any of those values. Would you mind telling me if you knew of what higher tier students are expected to know?
Could u make a highschool math exam of december from Belgium? From 11th grade, field of study ‘Wetenschappen Wiskunde’ or in english ‘Science-Math’ 11th grade is the hardest year in belgium and only a few people pass this math exam, the really smart people get like 60%. Average people get like 20%-30%. In my school only 2 people passed the 11th grade of this field of study and are now in 12th grade. Im in 11th and have to take this exam in december but i just heard its the most difficult exam in highschool
Sorry, guys: I'm being a super-grumpy old man tonight. At about 1:08:00 you both agree that, when looking at sin and cos, the graphs are helpful. I'm not a professional mathematician nor a maths communicator but I don't find squiggly lines terribly informative. Especially when it's super-hard to remember which starts at 0 and which starts at 1. On the other hand, the unit circle is easy to draw, to an acceptible level of accuracy. Then you only have to remember that cosine is the x axis value and sine is the y axis value and you are good to go. As a bonus, it reminds you that you get the same sine or cosine value every time around the circle.
Remember the small angle theorem. For small values of sin, the answer is approximately the value. So for zero, sin is zero. Makes drawing sin very easy. Or remember Tan is sin/cos, and that tangent is rise/run. Then picture the unit circle. When angle is zero the rise is o, the run is 1. So sin 0 = 0, cos 0 =1
the word perimeter CANNOT be applied to incomplete circles as they do not have a perimeter, they r just arcs with a specific length, so to ask for the arc length is the only valid question. to ask about the perimeter is like asking about the hight of a wooden rod -- as its cross section is round, there is no hight vs. width -- one might get what u talk about, but its _intrisicly wrong_
Did he imply that a student would be marked down if they proved it without using the alternative segment therom? Which is doable??? That hardly seems fair! Also discussion on the last question kind of annoyed me. I need to go back and see how they did it. None of that seemed necessary. All you really had to do is realize tan(30) is sin(30)/cos(30) and sin(30)=cos(60) and cos(30)=sin(60) Substitute and simplify to get cos(x)=cos(60). Would love to have seen the marking guide on that one. Edit: I went and looked at the marking guide, and I if I'm reading it right I would have gotten 0 marks for solving it the way I did, which is absolutely ridiculous in my opinion. But I would love to hear an argument as to why I'm wrong. I think an argument might be made that since I got tan(30)=sin(30)/cos(30) a kind hearted marker might have given me M1 but probably not since I didn't finish it off with (1/2)/(sqrt(3)/2) I still feel like their penalizing students that understand the relationship between the sin and cos of complementary angles. I mean change the numbers let's say they gave the equation cos(x)=sin(53) x tan(37). It's completely solvable without knowing the sin or cos of 53 or 37. Certainly they wouldn't expect you to know those values, but they still might expect you to be able to solve the problem. But because a student solved the problem they gave the same way they would solve this one, they are going to penalize them?
Watch me take the exam here: ruclips.net/video/hQVcv-T7IiY/видео.html
Lucky that RUclips recommended your video to me!!
This is great for 16 year olds to see math-expert adults working on their exams.
It was even better to see that the paper they did was exactly identical to the mock I had today 💀🤣
@@missachin5054 Is this really for 16 year olds? Seem extremely difficult.
@@kaspervestergaard2383 this is the easy stuff I’m gonna be honest 😂
@@missachin5054 Really? I know I'm bad at math, but this seems far from easy.
@@kaspervestergaard2383 this stuff is actually pretty easy, what grade are you in?
Discussing WHAT you should write down when answering exam questions is extremely useful to GCSE and A-level pupils. This video should be played in school Maths lessons. Thank-you so much.
To get top grade (grade 9) on AQA 2019 you needed to average around 86% across 3 exams that included this one. Both Tom and Ben got above 90% so were on course for a 9 :)
was refreshing seeing how people who've excelled in maths take on a GCSE paper, nice one!
My tutor gave me what was, for me at least, amazing advice when tackling exam papers. First thing you do, when the timer starts, put down all your stationery, and read through the paper. You will see many questions where you know you have the knowledge to at least tackle them, and also to do those ones first. If the first few questions happen to be ones that trip you up, you can get into a really anxious state so easily, when the rest of the paper may be fine for you. Going through the ones you're confident with first helps you settle so much better. Really helped me with my anxiety for exams :)
this is excellent advice!
To anyone taking a real exam and tends to refine their graphs by drawing it in multiple strokes like Tom does: draw and refine it in pencil first, then trace the final line in pen and erase your pencil sketch. Even if you’re unable to completely erase it, the single pen line removes any ambiguity about which exact line you consider to be your final answer, and that ambiguity is the biggest reason they deduct points for feathering.
When I was in school we would have gotten 0 marks if we drew a graph with pen lmao
@@wesleyml3682
Then use a heavy pencil stroke for the final line and erase the initial light strokes as best as you can. In any case, do your best to make it unambiguous.
What I use is a curve ruler to draw the graphs perfectly without feathering lol 😂🤣🤣
If it's a sketch, I'll just draw out the shape and label the points.
@@ragnkja Of course! That's what I'd do, for the times when there was any difficulty, of course. :) Thankfully those days are long gone and in university I only ever need to plot using R and Python.
It's pretty awe inspiring to see how a maths whizz brain works. Both you people are what I wished I was when doing O level maths all those years ago. Our young peoples maths progress is in good hands not just from your knowledge but your kindness and the way both of you are as human beings. Back in my day maths teachers instilled fear and were mostly grumpy, aggressive teachers that were only interested in the real high flyers of the class.
Got my mocks in 2 weeks, coming in clutch
Thanks Tom!
Good luck!
I'm out of school for 15 years and had nothing to do with math directly anymore. No idea how I got here but I really enjoyed doing the test along
awesome!
This is such a great video! I’m so glad I discovered your channel today, I know my students will find this kind of discussion incredibly useful! Keep up the fantastic content 😁🙏🏼
I totally agree. I dont use maths in my day to day job, but I do some at home out of passion. I had an absolute blast watching these videos and I'm sure that young students will too. The relaxed nature of the videos and seeing two teachers do what they will soon do in the future could be eye opening and motivating for them. Hope you'll have success with them
For the triangle and tangent problem, you could have also argued that the triangle can be cut down its symmetry line. That symmetry line is square to the remaining side AB. It's also a symmetry line of the circle, because it's a symmetric triangle in a circle = hits the center. So the same as the sqare line to the tangent in point C. AB is square to CO, CO is square to CD. = parallel.
Question 24 iand 27 are straight forward if you use the Unit circle.
And please note that the graphes that you two drew, are derived FROM the unit circle!
Now I'm just being a math teacher :) But hey, I LOVE this video!
Please do more..
The unavoidable q20. The mark scheme also allows the dropping of the perpendicular from C to the midpoint of AB through the circle centre (it's an isosceles triangle) and that goes through the centre of the circumscribed circle (symmetry, but easy to prove if you are bored). So you have a right angle with AB and a right angle at CD, so internal angles add up to two right angles, so you have two parallel lines.
Yeah. That line you can draw from C to the middle of AB is how i figured that one out. Once its there the rest is easy to spot the rest.
how to prove perpendicular from AB to C passes through center of circle?
@@navidtawsif9609 You'll need a pencil and paper to follow this: sorry. If only I could post pictures. This is might not be the simplest way to show that the perpendicular from the apex of an isosceles triangle to the opposite side goes through the centre of the circumscribed circle, but here goes:
Consider an isosceles triangle ABC, with AB = AC. Let the centre of the circumscribed circle be O, then OA = OB = OC because they are radii.
Triangles AOB ≅ AOC by SSS (AO = AO (shared), AC = AB (isosceles Δ) and OB = OC (radii)). Therefore ∠BAO = ∠CAO = ∠ABO = ∠ACO because of the congruence and Δs ABO and ACO are also isosceles (radii of the circumscribed circle). Let ∠BAO = α then ∠AOB = ∠AOC = (π - 2α)
Draw OM perpendicular to BC where M is on BC. OB = OC (radii), so ∠OBM = ∠OCM. ∠OMB = ∠OMC = 90° by construction. Therefore ∠BOM = ∠COM = (90° - ∠OBM). Now, ∠BOC = 2π - 2(π - 2α) = 4α. ∠BOM = ∠ COM = 2α.
∠AOB + ∠BOM = (π - 2α) + 2α = π therefore AOM is a straight line and AM is the perpendicular from A to BC that goes through O, the centre of the circumscribed circle. QED.
Edit: it might be quicker to assume the theorem that says the angle subtended by a chord at the centre of a circle is twice that subtended at the circumference. That gives you ∠BOC = 2∠BAC and then you draw OM and go from there. To prove that theorem, you basically do what I did above, so they are equivalent and my proof doesn't assume the angle at centre theorem.
What a brilliant video. Fantastic chemistry between you both, and super useful for students (or their teachers) in providing insights into the marking schemes used behind the scenes and therefore what is important. Well done do you both.
Our pleasure!
No chemistry here, it’s mathematics only.
Chemistry is an entirely different subject.
Chemistry.
@@dullaf4099 not funny
This is an amazing Maths conversation. Regarding Question 20. If you remove the Isoceles condition that AC=BC. Then the Chord formed by AB can go through a whole variety of angles to the tangent CD. If for instance AC is tiny and BC is maximised then the angle will be almost 90 degrees. Likewise is BC is tiny and AC is maximised it will be -90 degrees. If you imagine a whole series of possibilities for the chord AB it will form a continuum between +90 degrees and -90 degrees according to the different lengths of AC and BC. Halfway between these two possibilities (+90 degrees and -90 degrees) there must be some combination of lengths of AC and BC where then angle between the tangent CD and the Chord AB is zero (ie they are parallel) It makes sense for this to be halfway along the diffferent possibiilties for the lengths of AC and BC when they are equal. This seems intuitive reasoning to me but I am not sure whether this would be a good enough proof to get the marks in this question.
I find it so intresting as just went on a trip with my class and ended up seeing him give a talk, then I realised I already knew him from youtube. Loved the talk about how maths can save the environments keep up the good work.
Glad you enjoyed it today!!
Sorry about the excessive comments below. This was amazingly interesting. Blimey! Teachers marking these papers have a real job on their hands (I read the marking scheme because, well, OCD, probably). And the pupils taking these papers seem to have to learn an "exam language" where some keywords give a clue about what you need to do and in how much detail. I don't remember that from 40+ years ago when I was doing O levels (probably my age). I'll go now: I promise.
Great non-competitive math test video 👏👏
I just want to say that the last question is much easier than what you both thought:
Cos(x)= sin(60) x [sin(30)/cos(30)]
>> cos(x) cos(30)= sin(60) sin(30).
>> x= 60. {because cos(y)= sin(90-y)}
Read my comment, apparently you would have got 0 marks for this.
@@robertwoodruff8491 why is that?!
I’m 100% sure this correct, you can even prove it.
@@asamet2007 Did you read my other comment I posted? I say the exact same thing. I even go into further detail explaining how cos(x)=sin(53) x tan(37) couldn't be solved the way they did it, but can clearly be solved this way.
The problem is that the marking guide doesn't allow for it.
M1 in the marking guide basically says you have to come up with values for sin(60) or tan(30) or cos(30) and sin(30). You have to come up with the actual values.
M2 says once you have those values you have to use the values to find x. Writing down cos(x)=1/2 is enough to get the points on M2. But writing down cos(x)=cos(60) isn't. You can't get points on M2 without getting points for M1 it's "M1dep"
Then to get points for A1 you have to write down 60 AND get points for M2.
Don't believe me? Check out the marking guide: tomrocksmaths.files.wordpress.com/2021/10/aqa-83001h-w-ms-jun19.pdf
So no points for you or me. 😞
It's weird watching this now knowing I had sat this exam 3 years ago, doing it now and seeing the little mistakes I had done back then recorrected by myself. Great video series otherwise for people doing either gcse or a level maths seeing someone higher doing it
For cos(x) = sin(60).tan(30), you can solve by remembering tan = sin/cos and sin(90-x) = cos(x).
sin(60).tan(30) = sin(60).sin(30)/cos(30) = sin(60).cos(60)/sin(60) = cos(60).
Therefore x = 60, even if you don't know the values for sin and cos at those angles.
Parents (who are teachers) and School Teachers are the MOST IMPORTANT PEOPLE IN SOCIETY.
55:40(ish) Ben is correctly explaining the Alternate Segment Theorem: ACD = ABC. I'm pretty sure that, in his "doing the exam" video, he said ACD = BAC (which is, in general, wrong) and was worried about not having used the isosceles property of triangle ABC. That last fact is what makes ACD = BAC.
My suspicion is that Tom should not have awarded full marks here (Tom admits to not having followed the geometry - give the guy some slack: he's a brilliant mathematician but not a geometer). Perhaps I need to keep watching... (bad habit of commenting before the video ends)
Having worked through the mark scheme, I am so, so glad that I don't have to mark these papers.
Am totally loving this series of videos!! (Note to self: look out the A level ones).
You guys need to do another exam, this was great!
It was great to see that the paper they did was exactly identical to the mock I had today 💀🤣. Yes they should do another, perhaps I’ll get lucky again 🤣
We will - coming in 2022!
@@TomRocksMaths Do English and let's see if the rumours about either numbers or letters is true 😂
I remember an exam where first part was limits and second part was derivatives. Because the time was generous and I kinda knew I get trough the exam with spare time I decided to work it little differently. I first proved Hopital's method and used it to solve the limits. I got F from that part.
Yesss do a UKMT paper cuz it will be fun to see an oxford academic approach problem solving orientated questions
As a teacher, this was fantastic and useful!
glad you found it so!
I never thought I would like maths again after A-level and then Software engineering at uni but its kind of like car crash watching... I cant stop lol. Kudos Dr!
I mean that in a nice way btw I didn't mean it about your maths lol. Your both pretty amazing at your 1's and 2's
A question I’d love to see you solve is to find ‘r’ (sometimes written as ‘i’) in an annuity formula. I once tried to make each letter the subject in the formula, but got stuck with ‘r’, which appears twice, before being told by someone it cannot be done. I saw a video where a ‘brute force’ method was used to get an approximation of ‘r’, but I was quite confused as to what was going on. Yet it still baffles me why ‘r’ cannot be made the subject using factorisation and knowledge of algebra. The formula looks like this: A = P [(1+r)n -1/r] where n is a power. Pls consider solving this in a future video. By the way, really enjoy your videos and have learned a great deal from watching them.
Quadrilateral has 360 degrees because you can always divide it into two triangles.
Quite a surprize that you could not figuer this out ..
But I love the openess!
Bro shush
I definitely want to see you both attempt a Senior Math Challenge or BMO Round 1 exam! I think it'll be an interesting "not competition" if you don't immediately know how to solve every question haha
Yeah watching Tom and Ben do one of the UKMT papers would be really interesting, those things were my nemesis! 😨
The more advanced the questions the exams get, the easier it becomes for him to solve it. The only difficulty is him trying to remember basic maths equations to figure them out.
Ay, was doing some revision to keep up my knowledge during holiday and now you come out of knowhere. Thanks!
@38:00 A quick way to calculate the sum internal angles of any polygon is (n-2) * 180. Where n is the number of angles. Also for 3D geometry, F + V = E + 2, where F is the number of faces, V (vertices) and E (edges)
thx i didnt know that!
In Q20 I didn't use that fancy theorem,
I drew the perpendiular from C to the centre, so we have that the angle we care (the one equal to x and therefore the two lines are parallel) + another angle (let's call it y) is 90 deg.
Now y is an angle on the base of an isoceles tirangle with "big" angle 2x (it insits on the same point as the startign triangle and therefore is the double).
So y=(180-2x)/2=90-x but then 90=y + angle we care=90-x+angle we care=> angle we care=x
Re: sum of internal angles
I always imagine something I was shown as a kid where you just add a triangle to an existing shape such that a side matches and all the internal angles would still add up for the new shape and since you replaces one side with 2 it's a net change of +1 side.
Triangle + triangle = square, so must be 180°+180° = 360°
Square + triangle = pentagon, so a pentagon must be 360°+180°=540°
Etc.
I’ve been waiting for this video🤝👏
would love to see you attempt the A level Math paper from Singapore, especially the H2 and H3 levels... really want to hear your opinion on these papers especially given that they are set by the same cambridge authority as the international/uk A level and yet they are so so different from each other!
18:02 smooth catch
I'm glad someone noticed!
Great personalities very enjoyable to watch
Glad you enjoyed it :)
That was great fun, thank you both for taking the time to do that. Based on the tutoring that I have done, I think that's really useful for GCSE maths students to watch. (I couldn't agree more about the circle theorems, I hate the GCSE syllabus for doing this, what is it trying to achieve?)
Such a Great video!
One of the best Math videos out there..
I feel smart now I was 1 mark off a Dr of Maths score on a maths exam when I was doing my GCSEs
Ben, I totally agree with you on mixed integers and ratiometric fractions! They are as obsolete as Roman numerals. By all means leave ratios unsimplified to preserve accuracy during calculations, but there's no reason to describe something like 5/2 as anything besides 5/2 or 2.5. All real-life measuring instruments -- rulers, voltmeters, weighing scales ..... --- read decimal fractions anyway ..... #RealLifeIsDecimal
Also, "engineering notation" is a special form of exponential notation where the exponent is always a multiple of 3 so as to line up with a measurement prefix. For example, 589 * 10 ** -3 as opposed to 5.89 * 10 ** -7.
i remember when i learned about sin, cos, and tan we neither had those triangles nor any graphs. my teacher just gave us a paper and said "here are some important to know numbers for sin and cos. learn them" .... i don´t have to explain i already forgot those exact numbers, the only thing i remembered was "yeah sin60 was one of those numbers i had to learn"
Feathering penalty should be for students trying to sneak an obviously wrong answer through by having different lines go through different points and appear to be one graph. Here it was very clear what the intended line was. Harsh marking was harsh.
Grading scheme of a physics prof I had:
Perfect answer = 3 points
Perfect answer, no unit only in the final answer = 2 points
Anything else = 0 points
Person who disliked is the 4th friend who wasn't invited to the party
My faith in humanity has been restored. Nerds worldwide should do this stuff from AI/Machine Learning to Programming, Medicine, Quantum Computing, Law and Aircraft Technology.
For Q10, without marking/scoring guidance I had penalized Ben because he drew the curve all the way through x=5 and missed the correct value of Y(5) by 2. I’m glad to see the guidance is precise enough that it clearly states that this must be ignored.
This felt like a typical maths exam in Singapore.
Standard form is a number between 1 (inclusive) and LESS than BASE times a power of BASE. BASE in this case is 10. Floating point numbers (in computing) are the same format only the base is 2 and the power represents a shift value. (There's also a strange bias usually). The double line on the reciprocal graph (which I saw you making in the previous video) looked like an issue to me. Had you infilled it bold, you might have 'got away with it'. The simplify fully is a bit rough, but 4 and 6 do have a common factor... I somehow got to Comp Sci degree level without knowing the difference of squares identity, but I used the sum of squares identity months later in commercial programming to optimize multiply to 3 square look ups. I've been teaching my son some O-level maths and the alternate segment theorem cropped up. Again, news to me. It's said, you wouldn't ask Einstein to do a simple calculation, so the special case looks fine. Overall what strikes me most is that marking these things is way harder than doing them. I now have an appreciation that the marking system is remarkably fair. Nice video guys.
Letsss goooo, TOM you are an actual math giga chad
DCA = BAC due to "alternate angles" btw.
It would be interesting to see you do the Irish leaving certificate maths exam too
1:11:50-something. Tom asserts that he should have had the marks if he had differentiated (apparently not a GCSE thing - I have no idea, my maths O level (the then equivalent) was over 40 years ago). That reminds me of Mathologer (definitely a non-remunerated plug: subscribe to TRM and Mathologer and have multiple excuses to not do the washing up) who had, in uni, a proof rejected because it wasn't the one in the course (even though it was right).
Cool name
@@johngould3253 Haha - I blame my parents.
Please do videos about math high school and how to improve math skill in high school
I'm excited for another series! :D
Just remember that there are 2 triangles in a quadrilateral. So there are 360 degrees
Brilliant thanks both!
Can’t believe MGK and Russel Crowe are doing a collab
Writing really good questions and allocating marks is a highly refined skill.
Poorly written questions lead to poorly constructed mark schemes.
1 mark should be awarded per concept, calculation or demonstrated skill.
I love how both of you are complaining about GCSE "command words" the same way I am complaining about them in the German A-levels equivalent. Even worse, some of those are used in multiple subjects but mean slightly different things in each.
I would have awared the mark on the graph Q. I would look at it and think the students first line wasnt going through the points so he drew a second line and it wad clear you drew large crosses at the correct points to show the correct intend line. It is difficult to cross out graphs lines close together... definitely not gona penalise on that if I was an examiner
Hello Tom, it is fascinating to watch these kind of videos!
I live in Hong Kong and we have Public exam call the HKDSE. You should try doing it :)))). There are many practice paper or past paper in the Internet :)))
thanks - added to my list :)
i retook a maths paper higher the other day , ive been gone for 3 years now out of school and i still got a B which im shocked considering i forgot so much stuff
Do a video on the Irish leaving cert maths paper and compare to A level paper.
it's on my list, thanks!
TRY JEE ADVANCE MATHS paper
Called it out. Question 20 😎.
It's the sort of maths exam that Albert Einstein would fail. Imagine a top C++ programmer being asked to sit an exam on binary division calculated by hand or assemly language etc
Makes me feel better about only getting a C in maths
Fun fact: my teacher taught me the differentiate and i used it in the exam
30:17 here we go again...it says "the triangular CROSS SECTION of a prism", not "this is the whole prism". Hence the volume of the given triangular cross section is equal to 51cm^3.
the cross section of a solid is a figure/plane, it doesn't have a volume
I really wanted to do my ug studies at Oxford but unfortunately because of personal issues i couldn't. I hope that i can do higher education at Oxford
fingers crossed!
DO AN IB HL MATH PAPER!!!!
They’re easy
56 mins - alternate angles, not corresponding angles
Wonder if the good professor will try the Putnam Maths Exam?
Could u do AS level exam walk through pls?
I can't believe that you both still are complicating 20a) when it is dead obvious that a line from C to the midpoint of AB goes through the center of the circle and is therefore perpendicular to both AB and the tangent through C. (It does helps to draw the figure accurately).
Nice video. You should try a Scottish higher maths exam.
it's on the list :)
35:56 you can always split a quadrilateral into two triangles with 180 deg each, so it would be 360 deg for any quadrilateral
Just saw 38:01
Oh man do I have doosey of a video suggestion for you. -using Simpson’s method in order o find the centroid of an airfoil. -me and my senior design group were stumped for about 5 hours on it.
Love from Bangladesh 🖤🖤🖤
55:10 if you have an isosceles triangle inscribed in a circle, doesn't the line bisecting the triangle between the two equal-length sides necessarily pass through the centre of the circle? Which would make it perpendicular to the tangent line, and then the rest follows easily. Unless I've missed something here, it looks like the extremely wonky diagram they used has deliberately obfuscated what should be an intuitive fact
Awesome :)
Foundation tier students are expected to know sin cos tan of 30, 45, 60.
Wait really? I'm doing higher and I don't know any of those values. Would you mind telling me if you knew of what higher tier students are expected to know?
i know in edexcel you're expected to know sin, cos and tan for 0, 30, 45, 60, and 90 degrees. idk what aqa wants from you
52:31 Sparks Pog
Could you make a video on coaltz conjecture and reimaan's hypothesis :)
It'll be interesting to see those topics explained by you kkk
Moderator's meeting 😂😂😂
Pretty much!
Could u make a highschool math exam of december from Belgium? From 11th grade, field of study ‘Wetenschappen Wiskunde’ or in english ‘Science-Math’
11th grade is the hardest year in belgium and only a few people pass this math exam, the really smart people get like 60%. Average people get like 20%-30%. In my school only 2 people passed the 11th grade of this field of study and are now in 12th grade. Im in 11th and have to take this exam in december but i just heard its the most difficult exam in highschool
I think Tom's should be marked again by an independent Edexcel examiner for further controversy...Part III
agreed
Great video...
BTW from where did you get the T shirt in UK. It's really cool
I think this one was from Topman
Sorry, guys: I'm being a super-grumpy old man tonight. At about 1:08:00 you both agree that, when looking at sin and cos, the graphs are helpful. I'm not a professional mathematician nor a maths communicator but I don't find squiggly lines terribly informative. Especially when it's super-hard to remember which starts at 0 and which starts at 1.
On the other hand, the unit circle is easy to draw, to an acceptible level of accuracy. Then you only have to remember that cosine is the x axis value and sine is the y axis value and you are good to go. As a bonus, it reminds you that you get the same sine or cosine value every time around the circle.
Remember the small angle theorem. For small values of sin, the answer is approximately the value. So for zero, sin is zero. Makes drawing sin very easy.
Or remember Tan is sin/cos, and that tangent is rise/run. Then picture the unit circle. When angle is zero the rise is o, the run is 1. So sin 0 = 0, cos 0 =1
the word perimeter CANNOT be applied to incomplete circles as they do not have a perimeter, they r just arcs with a specific length, so to ask for the arc length is the only valid question. to ask about the perimeter is like asking about the hight of a wooden rod -- as its cross section is round, there is no hight vs. width -- one might get what u talk about, but its _intrisicly wrong_
Have you given O level a go from back in the day ?
Examiners being as generous as possible? Not in the US haha. They wanted us to fail. Then we would have to pay to take another test lol.
How do you mark at Oxford Tom?
Did he imply that a student would be marked down if they proved it without using the alternative segment therom? Which is doable??? That hardly seems fair!
Also discussion on the last question kind of annoyed me. I need to go back and see how they did it. None of that seemed necessary. All you really had to do is realize tan(30) is sin(30)/cos(30) and sin(30)=cos(60) and cos(30)=sin(60) Substitute and simplify to get cos(x)=cos(60). Would love to have seen the marking guide on that one.
Edit: I went and looked at the marking guide, and I if I'm reading it right I would have gotten 0 marks for solving it the way I did, which is absolutely ridiculous in my opinion. But I would love to hear an argument as to why I'm wrong. I think an argument might be made that since I got tan(30)=sin(30)/cos(30) a kind hearted marker might have given me M1 but probably not since I didn't finish it off with (1/2)/(sqrt(3)/2) I still feel like their penalizing students that understand the relationship between the sin and cos of complementary angles. I mean change the numbers let's say they gave the equation cos(x)=sin(53) x tan(37). It's completely solvable without knowing the sin or cos of 53 or 37. Certainly they wouldn't expect you to know those values, but they still might expect you to be able to solve the problem. But because a student solved the problem they gave the same way they would solve this one, they are going to penalize them?
Standard from is different in America
I didn't know that Machine Gun Kelly was also a mathematician?
side hustle
Face it Tom, after this you're enrolling to become a highschool teacher😂😂
Oh I couldn’t teach students that young. University for me.