Question

cos(а-П/2)-sin(a-П/2)​

Answer 1

cos(a - $\pi$/2) - sin (a - $\pi$/2) = cos(-($\pi$/2 - a) - sin(-($\pi$/2 - a) = cos($\pi$/2 - a) + sin($\pi$/2 -a) = sin(a) + cos(a)