Question

sin4x =4 sin x cos³x - cos x sin³x​

Answer 1

$cos^{2}θ=cos^{2}θ−sin^{2}θ$

$sin^{2}=2sinθcosθ$

$\fbox \green{ Then }$

$sin^{4}x=2sin^{2}x$

$cos^{2}x=2(2sinxcosx)$

$(cos^{2}x−sin^{2}x)$

$2(2sinxcosxcos2x−2sinxcosxsin^{2}x)$

$4sinxcos^{3}x−4sin^{3}xcos^{x}$

$\sf\large\pink{ Hope \: this \: will \: help \: you }$