Question

2cos²x/2=1+cosx+cos2x

Answer 1

$2cos^frac{x}{2}=1+cos x+cos (2x)$
$1+cos(2*frac{x}{2})=1+cos x+cos(2x)$
$1+cos x=1+cos x+cos(2x)$
$cos(2x)=0$
$2x=frac{pi}{2}+pi*k$
$x=frac{pi}{4}+frac{pi*k}{2}$
k є Z