Question

PLz help : Prove cos(2x)^2 = cos(4x).

Answer 1

let
\[x=\frac{\pi}{6}\] then
\[\cos^2(2\frac{\pi}{6})=\cos^2(\frac{\pi}{3})=(\frac{\sqrt{3}}{2})^2=\frac{3}{4}\] whereas
\[\cos(4\frac{\pi}{6})=\cos(\frac{2\pi}{3})=-\frac{1}{2}\] so it is not true