Q5 of 12 Page 595

If A + B + C = π, prove that


= cosA + cosB + cosC


Using ,




since A + B + C = π



And,





Using , cos2A = 1 – 2sin2A







= R.H.S


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3

If A + B + C = π, prove that

cos 2A – cos 2B + cos 2C = 1 – 4sin A cos B sin C


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If A + B + C = π, prove that

sin (B + C – A) + sin (C + A – B) – sin (A + B – C) = 4cos A cos B sin C