17. (sin 3A + sin A) sin A + (cos 3A - Cos A) cos A = 0
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(sin 3A +sin A) sin A+(cos 3A-cos A) cos =0
sinx+siny
=2sin(x+y/2) sin (x-y/2)
cosx -cosy
= 2sin (x+y/2) sin (x+y /2)
=(2sin 4A/2 cos 2A/2) sinA+(-2sin.4A/2 sin 2A/2)
=(2sin2A cos) sinA -2( sin2A.sin A) cos
=sin2x=2cosx.sinx
=sin 2A (sin 2A)-sin2A(sin 2A)
=0
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