Prove that : a cos A +b cos B+ c cos C=2 a sin B sin C

1.	Prove that : a cos A +b cos B+ c cos C=2 a sin B sin C
Answer» We know a / sin A = b / sin B = c / sin C. b = a cos C + c Cos A c = a Cos B + b cos ALHS = a cos A + (a cos C + c cos A) cos B + (a cos B + b Cos A) cos C = a cos A + cos A (c cos B + b Cos C) + 2 a Cos C Cos B = a cos A + cos A * a + 2 a cos C cos B = 2a [cos A + Cos C Cos B] = 2 a [ cos (π-B-C) + cos C cos B] = 2 a [- cos (B+C) + cos C cos B] = 2 a Sin B sin CRead more on Brainly.in - https://brainly.in/question/1122558#readmore

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