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Trigonometry

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Product-Sum Identity for $\cos{\alpha} \cos{\beta}$

TRIG-7OENS@

Which of the following equations correctly illustrates the Product-Sum Identity for $\cos{\alpha} \cos{\beta}$?

A

$\cfrac{1}{2} [\sin({\alpha} + {\beta}) + \sin({\alpha} - {\beta})]$.

B

$\cfrac{1}{2} [\cos({\alpha} + {\beta}) + \sin({\alpha} - {\beta})]$.

C

$\cfrac{1}{2} [\cos({\alpha} + {\beta}) + \cos({\alpha} - {\beta})]$.

D

$\cfrac{1}{2} [\sin({\alpha} + {\beta}) + \cos({\alpha} - {\beta})]$.