Russian Math Olympiad | A Very Nice Geometry Problem | Semicircle inside a quarter circle

Поделиться
HTML-код
  • Опубликовано: 14 янв 2025

Комментарии • 12

  • @marioalb9726
    @marioalb9726 14 часов назад +3

    Extremely easy:
    tanα = r/R= 5/10= 1/2 --> α= 26,565°
    x = 2R cos2α = 20*3/5= 12 cm

    • @RAG981
      @RAG981 13 часов назад +2

      Agree completely. But better to find tan2a = (1/2+1/2)/(1- 1/4) = 4/3, then cos 2a =3/5. More elegant.

  • @ناصريناصر-س4ب
    @ناصريناصر-س4ب 18 часов назад +8

    Let I be the center of the semicircle. We put

  • @jimlocke9320
    @jimlocke9320 17 часов назад

    At 3:25, construct AP. ΔAOP and ΔAQP are congruent by side-side-side. By congruency,

  • @giuseppemalaguti435
    @giuseppemalaguti435 17 часов назад +2

    L'ho risolto con la geometria analitica...la retta y=mx+10 è tangente alla circonferenza (x-5)^2+y^2=25..imponendo Δ=0,risulta m=-3/4..calcolo adesso il punto M,come intersezione tra y=(-3/4)x+10 e la circonferenza x^2+y^2=100=>M=(48/5,14/5).x=√((48/5)^2+(10-14/5)^2)=12

  • @xualain3129
    @xualain3129 15 часов назад

    10*cos(

  • @epsom2024
    @epsom2024 3 часа назад

    Draw a square AOBC.
    Let R be the intersection of straight lines BC and AN.
    AO:OP=PB:BR => BR=5/2
    AO:BR=4:1 , BN=y => (10+y):y=4:1 => y=10/3 , PQ:BR=2:1 => QN=2*BN=20/3

  • @murdock5537
    @murdock5537 12 часов назад

    PAO = QAP = δ → AM = AQ + MQ = 10 + (x - 10); AR = AO + RO = 20; sin⁡(BOR) = 1
    sin⁡(δ) = √5/5 → cos⁡(δ) = 2√5/5 → sin⁡(2δ) = 2sin⁡(δ)cos⁡(δ) = 4/5 →
    cos⁡(2δ) = 3/5 = x/20 → x = 12 → x - 10 = 2 = MQ; PM = √29

  • @RealQinnMalloryu4
    @RealQinnMalloryu4 6 часов назад

    (10)^2=100/90=1.10.1.2^5 1.2^1 2^1 (AMPO ➖ 2AMPO+1).

  • @nenetstree914
    @nenetstree914 18 часов назад +1

    12

  • @Anmol_Sinha
    @Anmol_Sinha 15 часов назад

    I am getting x as 12.5 lol
    So close yet so far