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So, I have to show that in a triangle, we have : (A, B, C are the angles of that triangle)

sinB+sinC-sinA=4cos(A/2)sin(B/2)sin(C/2)

okay, here is what I got to, then I got stuck

i got it equal to:

sinB+sinC-sinA = 2cos(A/2)cos(B/2)cos(C/2)+2cos(A/2)sin(B/2)sin(C/2)-2sin(B/2)sin(C/2)

I don't know what to do next! Any hints?

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# Homework Help: Stuck :s

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