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If A+B+C=180^@ prove that: sin(B+2C)+sin...

If `A+B+C=180^@` prove that: `sin(B+2C)+sin(C+2A)+sin(A+2B)= 4 sin((B-C)/2)sin((C-A)/2)sin((A-B)/2)`

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PATHFINDER-TRIGONOMETRIC RATIOS AND IDENTITIES-QUESTION BANK
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