Phương trình \(\cos 2\left( {x + {\pi  \over 3}} \...

Câu hỏi: Phương trình \(\cos 2\left( {x + {\pi  \over 3}} \right) + 4\cos \left( {{\pi  \over 6} - x} \right) = {5 \over 2}\) có nghiệm là:

A \(\left[ \matrix{x = - {\pi \over 6} + k2\pi \hfill \cr x = {\pi \over 2} + k2\pi \hfill \cr} \right.\,\,\,\,\left( {k \in Z} \right)\)

B \(\left[ \matrix{x = {\pi \over 6} + k2\pi \hfill \cr x = {{3\pi } \over 2} + k2\pi \hfill \cr} \right.\,\,\,\,\left( {k \in Z} \right)\)

C \(\left[ \matrix{x = - {\pi \over 3} + k2\pi \hfill \cr x = {{5\pi } \over 6} + k2\pi \hfill \cr} \right.\,\,\,\,\left( {k \in Z} \right)\)

D \(\left[ \matrix{x = {\pi \over 3} + k2\pi \hfill \cr x = {\pi \over 4} + k2\pi \hfill \cr} \right.\,\,\,\,\left( {k \in Z} \right)\)