Prove that cos²2x-cos²6x=sin4x.sin8x
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Answer:
L H.S=cos^2 2x-cos^2 6x
=(1-sin^2 2x)-(1-sin^2 6x)
=sin^2 6x-sin^2 2x
= sin(6x+2x)sin(6x-2x)
=sin 8x sin 4x
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