Trigonify

Sum to Product

cos A - cos B

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

Related Sum to Product identities

sin A + sin Bsin A - sin Bcos A + cos B

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