Question

Verify the identity.

cos 4x + cos 2x = 2 - 2 sin2 2x - 2 sin2 x

Answer 1

I don't get why "verify" and then "increasing" "decreasing"
hey, why do you delete your comments?

Answer 2

because it wasnt related to the question

Answer 3

\(\text{Proof that }\cos4x+\cos2x=2-2\sin^2 2x-2\sin^2 x\\\)
\(=2-2\left [{1-\cos4x\over2} \right ]-2\left [{1-\cos2x\over2} \right ]\\\)
\(=2-\left (1-\cos4x \right )-2\left (1-\cos2x \right )\\\)
\(=\cos4x +\cos2x\\\)

Answer 4

Let me know if you have any questions.

Answer 5

did you use a formula

Answer 6

The only formula used was the half-angle formula:
\(\large \sin^2 x={1-\cos2x\over2}\).

Have you seen this?

Answer 7

no i havent