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posted by Mike on Wednesday, May 26, 2010 at 9:40pm.
Prove that sin(A+B+C+)cos(B+C)-cos(A+B+C)sin(B+C)=sinA
recall that sinPcosQ - cosPsinQ = sin(P-Q) LS = sin(A+B+C+)cos(B+C)-cos(A+B+C)sin(B+C) = sin((A+B+C) -(B+C)) = sinA = RS
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