Question

Help please

Verify the identity.

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

Answer 1

cos 4x = 2cos^2 2x - 1
cos 2x = 2cos^2 x -1
result:2-2sin^ 2x - 2sin^2 x

Answer 2

so 2cos^2 2x - 1 + 2cos^2 2x - 1= 2-2sin^ 2x - 2sin^2 x?

Answer 3

do you know how to express \(\cos(2x)\) in terms of \(\sin(x)\)?

Answer 4

using the double-angle formulae

Answer 5

yes , you should first optimize it wheter you know double angle formulas or not?

Answer 6

so am I right then? That so 2cos^2 2x - 1 + 2cos^2 2x - 1= 2-2sin^ 2x - 2sin^2 x?

Answer 7

yes , it was great