prove that
. sin (n + 1)x sin (n + 2)x + cos (n + 1)x cos (n + 2)x = cos x
(BT
(3т
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the whole step by step proof is given in the picture
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Step-by-step explanation:
L.H.S = sin(nx+x).sin(nx+2x) + cos(nx+X).cos(nx+2x)
=cos(nx+X).cos(nx+2x) + sin(nx+x).sin(nx+2x)
=cos(nx+x-nx-2x)
=cos(-x)
=cos x
=R.H.S
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