Prove that: cos 4x = 1 – 8sinx cosx

Asked by Abhisek | 1 year ago |  83

##### Solution :-

Consider

LHS = cos 4x

We can write it as

= cos 2(2x)

Using the formula cos 2A = 1 – 2 sin2 A

= 1 – 2 sin2 2x

Again by using the formula sin2A = 2sin A cos A

= 1 – 2(2 sin x cos x) 2

So we get

= 1 – 8 sin2x cos2x

= R.H.S.

Answered by Pragya Singh | 1 year ago

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