Question

Verify the identity.

cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x

Answer 1

OUCH...tis a tough one! first eqn u need is cos(2A) = cos^2(A) - sin^2(A)

use that to change the cos 4x into cos^2 2x and sin^2 2x okay?

Answer 2

Do you know Euler's identity?

Answer 3

cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x

Answer 4

@superdavesuper

Answer 5

you need this identity :
cos(2x) = 1 - sin^2 (x)

now can you identify for cos(4x)
cos(4x) = cos(2 * (2x)) = ... ?

Answer 6

oppps i mean
cos(2x) = 1 - 2 sin^2 (x)

Answer 7

cos 4x = cos 2(2x) and then use the general formula cos 2A = cos^2 (A) - sin^2 (A) to convert....