Question

Cos2x*1/2=?
Очень важно!

Answer 1

$cos2x*\frac{1}{2} =\frac{cos2x}{2}=\frac{cos^2x}{2} -\frac{sin^2x}{2} =\\\\=sin(\frac{\pi}{4} -x)sin(x+\frac{\pi}{4} )$