sin4xsin2x=-1/2[cos(4x+2x)/2-cos(4x-2x)/2]=-1/2(cos3x-cosx)
sinxsin3x=-1/2[cos(x+3x)/2-cos(x-3x)/2]=-1/2(cos2x-cosx)
sin4xsin2x-sinxsin3x
=[-1/2(cos3x-cosx)]-[-1/2(cos2x-cosx)]
=1/2(cos2x-cos3x)
=1/2*[(-2)sin(2x+3x)sin(2x-3x)]
=-sin5xsin(-x)
=sinxsin5x