Cho hàm số \(f\left( x \right)={{\cos }^{2}}\left(...

Câu hỏi: Cho hàm số \(f\left( x \right)={{\cos }^{2}}\left( \frac{\pi }{3}-x \right)+{{\cos }^{2}}\left( \frac{\pi }{3}+x \right)+{{\cos }^{2}}\left( \frac{2\pi }{3}-x \right)\) \(+{{\cos }^{2}}\left( \frac{2\pi }{3}+x \right)-2{{\sin }^{2}}x\). Hàm số có f’(x) bằng:

A  6                                            

B  2sin2x                        

C 0                                             

D  2cos2x