If A+B+C=pi, prove that sinA+sinB+sinC=4 cos A/2 cos B/2 cos C/2

Asked by  | 4th Dec, 2012, 05:46: PM

Expert Answer:

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

Answered by  | 5th Dec, 2012, 01:06: AM

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