Question:
prove that cos22x - cos26x = sin4x sin8x.
Answer:
We need to prove : cos22x - cos26x = sin4x sin8x
L.H.S. = (cos2x - cos6x)(cos2x + cos6x)
(-2sin4xsin(-2x))(2cos4xcos2x)
(2sin2xcos2x)(2sin4xcos4x)
sin4x sin8x = RHS
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