I know i'm supposed to use double angle formula, but i still don't get how to get my answer. I am to Express cos^2 (2x) in terms of cos 4x.(Crying)

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- May 13th 2012, 05:18 AMjohnrealExpress cos^2 (2x) in terms of cos 4x
I know i'm supposed to use double angle formula, but i still don't get how to get my answer. I am to Express cos^2 (2x) in terms of cos 4x.(Crying)

- May 13th 2012, 05:20 AMProve ItRe: Express cos^2 (2x) in terms of cos 4x
Do you know that $\displaystyle \displaystyle \begin{align*} \cos{2\theta} &\equiv 2\cos^2{\theta} - 1 \end{align*}$? Let $\displaystyle \displaystyle \begin{align*} \theta = 2x \end{align*}$.

- May 13th 2012, 05:27 AMjohnrealRe: Express cos^2 (2x) in terms of cos 4x
Is it + 1 or -1 at the end?

- May 13th 2012, 06:00 AMProve ItRe: Express cos^2 (2x) in terms of cos 4x