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 Question from Sam: 1. express the following as a trigonometric function of angle x for cos (3pi/2 -x) the answer in the textbook is -sin x but i am unsure of the process to get the answer.

Hi Sam,

I would use the identity

$\cos(a+b) = \cos(a)\cos(b) - \sin(a)\sin(b) \mbox{ with } a = \frac{3 \pi}{2}, b = -x.$

Write back if you need more assistance,
Penny

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