Hi Mr. G. So I'm still just a little confused here with "express () as trig function of angle x" questions. For example,

sin(pi + x) = -sinx

cos(pi/2 + x) = -sinx

I understand using the equivalent expression rules to solve these. What I'm confused about is what dictates the sign (+ or -). For example in the cos(pi/2 + x) problem, the terminal arm is in quadrant 2, so sin is positive in that quadrant. Yet still the answer is -sinx. Is it the original cosine part of the problem that dictates the CAST?