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

If `A + B + C = 180^(@)` prove that:
(i) `"sin" (B+C-A) + "sin"(C+ A-B)`
`+ sin (A + B-C) = 4 sin A sin B sin C`
(ii) `cos(- A+B+C) + cos (A - B + C)`
`+ cos (A + B - C) = 1 + 4 cos A cos B cos C`
(iii) `"tan" (B+C - A) + tan (C+A-B)`
`+ tan (A + B-C)`
` = tan (B+C - A) tan (C+ A - B) tan (A+B-C)`

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