Question 707070
Use the identity:
{{{ sin(A+B)=sinAcosB+cosAsinB }}}
giving {{{ sin2A=2sinAcosA }}}, or, {{{ sinxcosx =(1/2)sin2x}}}


So then:
{{{ (sinx)(cosx)(cos 2x) =(1/2)sin2xcos2x=(1/4)sin4x }}}