Question

cos (pi/2 +x) cosx+ sin (pi/2+x)sinx=0

Answer 1

$cos( frac{pi}{2} + x) cos(x) + sin(frac{pi}{2} + x) sin(x) = 0 \ \ - sin(x) cos(x) + cos(x) sin(x) = 0 \ \ cos(x) sin(x) - cos(x) sin(x) = 0 \ \ 0 = 0$