[tex]\sec \theta = \sqrt 2\\\\\implies \cos \theta = \dfrac 1{\sqrt 2}\\\\\implies \theta = 2n\pi \pm \dfrac{\pi}4\\\\\\\text{In the interval}~ 0 < \theta < 2\pi, \\\\\theta = \dfrac{\pi}4, \dfrac{7\pi}4~~ \text{or}~~ \theta = 45^{\circ}, 315^{\circ}[/tex]
