Trigo Triangle Question

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Sep 24, 2012
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In Triangle ABC, prove that cosA + cosB + cosC = 1 + 4sin(A/2)sin(B/2)sin(C/2).

I've tried the 3 basic trigo formulas for triangles but they always end up in some dead end, but I'm guessing that only these 3 are needed because this is a 'basic' question so I don't think complex formulas are needed. Thank you!
 
In Triangle ABC, prove that cosA + cosB + cosC = 1 + 4sin(A/2)sin(B/2)sin(C/2).

I've tried the 3 basic trigo formulas for triangles but they always end up in some dead end, but I'm guessing that only these 3 are needed because this is a 'basic' question so I don't think complex formulas are needed. Thank you!

Are you supposed to assume that m(A) + m(B) + m(C) = pi? If so, then this might interest you. :wink:
 
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