SOLUTION: Which sum or difference identity would you use to verify that cos(90 + theta) = -sin(theta)?

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Question 1012725: Which sum or difference identity would you use to verify that cos(90 + theta) = -sin(theta)?
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
cos(a + b) = cos a * cos b - sin a * sin b