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If A+B-C=3pi,\ t h e n\ sin A+ sin B-...

If `A+B-C=3pi,\ t h e n\ sin A+ sin B-sin C` is equal to-
a.`4sin(A/2)sin(B/2)cos(C/2)`
b. `-4sin(A/2)sin(B/2)cos(C/2)`
c.`\ 4cos(A/2)cos(B/2)cos(C/2)`
d. `-4cos(A/2)cos(B/2)cos(C/2)`

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