$$\left. \begin{array} { l } { \sqrt { 2 } \cos x - 1 = 0 } \end{array} \right.$$
$x=2\pi n_{1}+\frac{\pi }{4}\text{, }n_{1}\in \mathrm{Z}$
$x=2\pi n_{1}+\frac{7\pi }{4}\text{, }n_{1}\in \mathrm{Z}$
