Q. 24

# Mark the Correct alternative in the following:2(1 – 2 sin2 7x) sin 3x is equal toA.sin 17x – sin 11xB. sin 11x – sin 17xC. cos 17x – cos 11xD. cos 17x + cos 11x

Given expression is 2(1 – 2 sin2 7x) sin 3x

2(1 – 2 sin2 7x) sin 3x = 2 cos 2(7x) sin 3x

[ using cos 2A = 1 – 2sin2A ]

= 2 cos 14x sin 3x

[using the sum of angles formula ] = sin (17x) – sin (11x)

Therefore 2(1 – 2 sin2 7x) sin 3x = sin (17x) – sin (11x)

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