Question

cosx-sin3x=cos2x,find the value of x.
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Answer 1

Answer: Given that cosx-sin3x=cos2x then

⇒cos x - sin 3x = cos 2x

⇒cos x - sin (90-3x) = cos 2x

⇒cos x - cos 90 - 3x = cos 2x

⇒x - 90 - 3x = 2x

⇒-90 = 2x + 3x - x

⇒-90 = 4x

⇒x = - 90/4

⇒x = - 22.5

thus value of x = - 22.5

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