Trigonometry
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Sum to Product: cos A − cos B

Sum-to-product identity.

Formula

cos⁡A−cos⁡B=−2sin⁡A+B2sin⁡A−B2\cos A - \cos B = -2\sin\tfrac{A+B}{2}\sin\tfrac{A-B}{2}

Variables

A,BAngles

Did You Know?

Subtracting two cosines produces a product that engineers exploit in signal demodulation.

sum to productidentity