Giải phương trình cos ( 5x + pi /3) + 1 = 0

Lời giải:

\(\cos \left( {5x + \frac{\pi }{3}} \right) + 1 = 0\)

\( \Leftrightarrow \cos \left( {5x + \frac{\pi }{3}} \right) = - 1\)                                            

\( \Leftrightarrow 5x + \frac{\pi }{3} = \pi + k2\pi \,\,\,\left( {k \in \mathbb{Z}} \right)\)

\( \Leftrightarrow x = \frac{{2\pi }}{{15}} + k\frac{{2\pi }}{5}\,\,\left( {k \in \mathbb{Z}} \right)\).