If A + B + C = {270^o}, then cos ,2A + cos 2B | vedclass

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Question

(b) $A + B + C = {270^o}\,\,\, \Rightarrow A = B = C = {90^o},$ then 

$\cos 2A + \cos 2B + \cos 2C + 4\sin A\,\sin B\,\sin C$

$ = \cos {180

Vedclass · Accepted Answer

$1$

Vedclass · Answer

(b) $A + B + C = {270^o}\,\,\, \Rightarrow A = B = C = {90^o},$ then 

$\cos 2A + \cos 2B + \cos 2C + 4\sin A\,\sin B\,\sin C$

$ = \cos {180^o} + \cos {180^o} + \cos {180^o} + 4\sin {90^o}\sin {90^o}\sin {90^o}$

$ = - 1 - 1 - 1 + 4 \cdot 1\cdot 1\cdot 1 = - 3 + 4 = 1$.

If $A + B + C = {270^o},$ then $\cos \,2A + \cos 2B + \cos 2C + 4\sin A\,\sin B\,\sin C = $

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