Phương trình cosx = cos pi /6 có nghiệm là

\(x = \frac{\pi }{6} + k\pi ;\,\,\,x = - \frac{\pi }{6} + k\pi \,\left( {k \in \mathbb{Z}} \right)\).

\(x = \frac{\pi }{6} + k2\pi ;\,\,x = - \frac{\pi }{6} + k2\pi \,\left( {k \in \mathbb{Z}} \right)\).

\(x = \frac{\pi }{6} + k2\pi ;\,\,x = \frac{{5\pi }}{6} + k2\pi \,\left( {k \in \mathbb{Z}} \right)\).

\(x = \frac{\pi }{6} + k\pi ,\left( {k \in \mathbb{Z}} \right)\).