cos 4x = 1-8sin²x*cos²x – InterviewSolution

1.

cos 4x = 1-8sin²x*cos²x

Answer»

cos4x as

cos2(2x) =1-2sin²(2x)

=1-2(2sinx . cosx)² { sin2x = 2sinx. cosx}

=1-2(4sin²x.cos²x)

=1-8sin²x.cos²x

LHS=RHS

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