Question

cos( π/2-х/2)-3cos( π-х/2)=0

Answer 1

$cos(frac{pi}{2}-frac{x}{2})=sinfrac{x}{2}\\cos(pi -frac{x}{2})=-cosfrac{x}{2}\\sinfrac{x}{2}+3cosfrac{x}{2}=0|:cosfrac{x}{2}ne 0\\tgfrac{x}{2}+3=0\\frac{x}{2}=-arctg3+pi n,; nin Z\\x=-2arctg3+2pi n,; nin Z$