## Itel 2 years ago Help please Verify the identity. cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x

1. shining

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

2. Itel

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

3. asnaseer

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

4. asnaseer

using the double-angle formulae

5. shining

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

6. Itel

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

7. shining

yes , it was great