The product of the first three factors (terms) is 2*sin(3x)*cos(3x) = sin(6x). The fourth term is 2*cos^2(3x)-1 = cos(6x). Therefore 2*sin(3x)*cos(3x)*(2cos^2 3x-1) = sin(6x)*cos(6x) = (1/2)*sin(12x). ANSWER