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Product-to-sum identities

Revision as of 19:26, 7 September 2023 by Yiyj1 (talk | contribs) (Created page with "The product-to-sum identities are as follows: <math>\sin (x) \sin (y) = \frac{1}{2} (\cos (x-y) - \cos (x+y))</math> <math>\sin (x) \cos (y) = \frac{1}{2} (\sin (x-y) + \sin...")
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The product-to-sum identities are as follows:

$\sin (x) \sin (y) = \frac{1}{2} (\cos (x-y) - \cos (x+y))$ $\sin (x) \cos (y) = \frac{1}{2} (\sin (x-y) + \sin (x+y))$ $\cos (x) \cos (y) = \frac{1}{2} (\cos (x-y) + \cos (x+y))$ They can be derived by expanding out $\cos (x+y)$ and $\cos (x-y)$ or $\sin (x+y)$ and $\sin(x-y)$, then combining them to isolate each term.

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