Question

Verify the identity.

cos 4u = cos22u - sin22u

Answer 1

4u=2u+2u

Answer 2

Oh, sorry. The problem is \[\cos4u=\cos^22u-\sin^22u\]

Answer 3

@Jonask

Answer 4

use the identity\[\cos 2\theta=\cos^2\theta-\sin ^2\theta\]
\[\cos 2(2u)=?\]

Answer 5

cos 2u=cos^2u-sin^2u
then cos 2(2u)= cos^2(2u)-sin^2(2u)

Answer 6

Oh ok. Then what do I do? Subtract cos^2(2u)?

Answer 7

@jishan