Answer :

Take L.H.S:







{sin (-A) = - sin A}











{sin (-A) = - sin A}




= R.H.S.


Hence Proved


ii. Take L.H.S.:


cos(A + B + C) + cos (A – B + C) + cos(A + B – C) + cos(-A + B + C)


= {cos (A + B + C) + cos (A – B + C)} + {cos (A + B – C) + cos (-A + B + C)}







= 2 cos (A + C) cos B + 2 cos B cos (A – C)


= 2 cos B {cos (A + C) + cos (A – C)}






= 4 cos A cos B cos C


= R.H.S.


Hence Proved


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