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Possible Duplicate:
Prove that $\sin(2A)+\sin(2B)+\sin(2C)=4\sin(A)\sin(B)\sin(C)$ when $A,B,C$ are angles of a triangle
Prove trigonometry identity?

If $A$, $B$, and $C$ are to be taken as the angles of a triangle, then I beg someone to help me the proof of $$\sin A + \sin B + \sin C = 4 \cos \frac{A}{2} \cos \frac{B}{2} \cos \frac{C}{2}.$$ Thanks!

  • 0
    Hint: $A=180^{\circ}-(B+C)$2012-08-09
  • 0
    Relevant: http://math.stackexchange.com/questions/176892/prove-trigonometry-identity/176915#1769152012-08-09

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