sinx(x/2)cos(x/2)*cos(x)
=1/2*(2*sin(x/2)*cos(x/2))*cos(x)=1/2*sin(x)*cos(x)=1/4*(2*sin(x)*cos(x))=1/4*sin(2x)
sinx(x/2)cos(x/2)*cos(x)==1/2*(2*sin(x/2)*cos(x/2))*cos(x)=1/2*sin(x)*cos(x)=1/4*(2*sin(x)*cos(x))=1/4*sin(2x)