Tìm nguyên hàm (x.cos2x.dx): 1/2x . sin2x - 1/4.cos2x + C

A. $\frac{1}{2}x.\sin 2x-\frac{1}{4}\text{cos2x+C.}$

B. $x.\text{sin2}x+\cos \text{2}x+C.$

C. $\frac{1}{2}x\sin 2x+\frac{1}{2}\text{cos2}x+C.$

D. $\frac{1}{2}x.\sin 2x+\frac{1}{4}\text{cos2}x+C.$