cos(alpha - beta) cos(alpha + beta) = cos squared alpha - sin squared beta
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Originally Posted by Valaina cos(alpha - beta) cos(alpha + beta) = cos squared alpha - sin squared beta use the sum/difference identity for cosine ... $\displaystyle \cos(a \pm b) = \cos(a)\cos(b) \mp \sin(a)\sin(b)$ btw ... this should have been posted in the trig section.
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