Cực trị của hàm số y = sin2x – x là
A. ${{x}_{{C\text{D}}}}=\frac{\pi }{6}+k2\pi ;\begin{array}{*{20}{c}} {} & {{{x}_{{CT}}}=-\frac{\pi }{6}+k2\pi \begin{array}{*{20}{c}} {} & {(k\in Z)} \end{array}} \end{array}$
B. ${{x}_{{C\text{D}}}}=\frac{\pi }{3}+k2\pi ;\begin{array}{*{20}{c}} {} & {{{x}_{{CT}}}=-\frac{\pi }{3}+k2\pi \begin{array}{*{20}{c}} {} & {(k\in Z)} \end{array}} \end{array}$
C. ${{x}_{{C\text{D}}}}=\frac{\pi }{6}+k\pi ;\begin{array}{*{20}{c}} {} & {{{x}_{{CT}}}=-\frac{\pi }{6}+k\pi \begin{array}{*{20}{c}} {} & {(k\in Z)} \end{array}} \end{array}$
D. ${{x}_{{C\text{D}}}}=\frac{\pi }{3}+k\pi ;\begin{array}{*{20}{c}} {} & {{{x}_{{CT}}}=-\frac{\pi }{3}+k\pi \begin{array}{*{20}{c}} {} & {(k\in Z)} \end{array}} \end{array}$