sin^22θ+2cos^2θcos2θ=2cos^2θ

sin^22θ+2cos^2θcos2θ=2cos^2θ

sin²2θ+2cos²θcos2θ
=(2sinθcosθ)²+2cos²θ(1-2sin²θ)
=4sin²θcos²θ+2cos²θ-4sin²θcos²θ
=2cos²θ