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NCERT Class XI Mathematics - Trigonometric Functions - Solutions

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Question : 30 of 61
Marks: +1, -0
cos2cos^2 2x – cos2cos^2 6x = sin 4x sin 8x
Solution:  
We have, L.H.S.= cos2cos^2 2x – cos2cos^2 6x
= sin(2x + 6x) sin(6x – 2x)
[Since cos2A−cos2Bcos^2 A - cos^2 B = sin (A + B) sin (B - A)]
= sin(8x) sin(4x) = R.H.S.
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