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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