Tìm\(\int{x\cos 2x\,\text{d}x}.\)

Câu hỏi: Tìm\(\int{x\cos 2x\,\text{d}x}.\)

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

B \(x.\operatorname{s}\text{in2}x+\cos \text{2}x+C.\)           

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

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