Answer
$$\int x\,cos2x\,dx=\frac{x}{2}sin2x+\frac{1}{4}cos\,2x+C$$
Work Step by Step
$${(\frac{x}{2}sin2x)}'=\frac{1}{2}sin2x+x\,cos2x$$
$$\int x\,cos2x\,dx=\frac{x}{2}sin2x-\frac{1}{2}\int sin2x\,dx$$
$$=\frac{x}{2}sin2x+\frac{1}{4}cos\,2x+C$$