Tricky Trigonometry! | 3cos(2x) = sin(x) - 2 - Here's the Solution!

[@UgochihopeOgwa]

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[@KolbilFelix]

Just subscribed

[@NonsoMaths]

Thanks a lot!

[@mekings0422]

This is awesome .. brought back memories

[@NonsoMaths]

Happy memories, I hope. 🙂
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[@mekings0422]

@ mixed feelings lol .. but mostly happy memories

[@NonsoMaths]

Alright. I wish you a great day.

[@cyruschang1904]

cos(2x) = 2(cosx)^2 - 1 = 2(1 - (sinx)^2) - 1 = 1 - 2(sinx)^2
3cos(2x) = 3 - 6(sinx)^2 = sinx - 2
6(sinx)^2 + sinx - 5 = 0
(sinx + 1)(6sinx - 5) = 0
sinx = -1 or 5/6
x = 3π/2 + 2πn = π(2n + 3/2)
or
x = arcsin(5/6) + 2πn

[@NonsoMaths]

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[@cyruschang1904]

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[@KolbilFelix]

Please,why can't you say that sin90-2x is equal to cos2x.