$$2n\pi ;\,n = 0,\, \pm 1,\, \pm 2....$$

$$x = 2n\pi + \pi /2;\,n = 0,\, \pm 1,\, \pm 2....$$

$$x = n\pi + {\left( { - 1} \right)^n}\,\,\,\,\,\,\,{\pi \over 4} - {\pi \over 4}$$ ; $$n = 0,\, \pm 1,\, \pm 2..$$

none of these