Giải hệ phương trình \(\left\{ {\begin{array}{*{20}{c}}{x - y = \frac{\pi }{3}}\\{{\rm{cosx - }}\cos y = - 1}\end{array}} \right.\).

A.0     

B.1     

C.2      

D.4

A.\[ - \frac{{5{\pi ^2}}}{{12}}\]

B. \[ - \frac{{5{\pi ^2}}}{{144}}\]

C. \[\frac{{5{\pi ^2}}}{{144}}\]

D. \[\frac{{{\pi ^2}}}{{12}}\]

A.\[m \ne \frac{1}{2}\]

B. \[m = \frac{1}{2}\]

C. \(\left\{ {\begin{array}{*{20}{c}}{\frac{1}{3} < m < 1}\\{m \ne \frac{1}{2}}\end{array}} \right.\)

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D. \[\frac{1}{3} < m < 1\]

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A.\(\left[ {\begin{array}{*{20}{c}}{x = \frac{{k\pi }}{2}}\\{x = \pm \frac{1}{2}arccos( - \frac{1}{6}) + k\pi }\end{array}} \right.(k \in Z)\)

B. \(\left[ {\begin{array}{*{20}{c}}{x = \frac{{k\pi }}{2}}\\{x = \pm \frac{5}{2}arccos( - \frac{1}{6}) + k\pi }\end{array}} \right.(k \in Z)\)

C. \(\left[ {\begin{array}{*{20}{c}}{x = \frac{{k\pi }}{2}}\\{x = \pm \frac{1}{2}arccos( - \frac{1}{3}) + k\pi }\end{array}} \right.(k \in Z)\)

D. \(\left[ {\begin{array}{*{20}{c}}{x = \frac{{k\pi }}{2}}\\{x = \pm \frac{1}{3}arccos( - \frac{1}{6}) + k\pi }\end{array}} \right.(k \in Z)\)

A.0

B.1     

C.2

D.3

A.m=1

B.Không có m

C.m=0

D.Với mọi m

A.\[\left| a \right| \ge 1\]

B. \[\left| a \right| >1\]

C. \[\left| a \right| = 1\]

D. \[\left| a \right| \ne 1\]