Question

Verify the identity.

cos(x+π/2) = -sin x

Answer 1

hint:

cos(A+B) = cos(A)cos(B) - sin(A)sin(B)

replace "A" with x and "B" with pi/2

and you'll see for yourself that it equals - sinx

Answer 2

cos(x)cos(pi/2) - sin(x)sin(pi/2) = cosx(0) - sinx(1) = 0-sinx so -sinx? Did I do it right?!?!?!

Answer 3

very good!

Answer 4

Thank you!