Question

cos((pi/2) + x) = -sin x

Answer 1

verify the identity

Answer 2

use the sum identity for cosine

Answer 3

cos(a+b)=cos(a)cos(b)-sin(a)sin(b)

Answer 4

so I got cos(x+pi/2) = cosx cos(pi/2) - sin x sin(pi/2) where sin(pi/2) is then equal to 1, but what happens to the rest of the equation?

Answer 5

cos(pi/2)=0

Answer 6

so you have exactly what you need and want

Answer 7

Thanks so much!