SOLUTION: verify the identity cos (x + pi/2) = -sin x

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Question 772825: verify the identity
cos (x + pi/2) = -sin x
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
cos+%28x+%2B+pi%2F2%29=cos%28x%29cos%28pi%2F2%29-sin%28x%29sin%28pi%2F2%29

then we can write

cos%28x%29%2A0-sin%28x%29%2A1=-sin%28x%29