Consider the function $f(x,y)=1-cosx+\frac{y^2}{2}.$ Find all critical points $of$

$f(x,y).$

dots,$(-2,0),(-,0),(0,0),(,0),(2,0),(3,0),$dots

dots,$(-\frac{3}{2},0),(-\frac{}{2},0),(0,0),(\frac{}{2},0),(\frac{3}{2},0),(\frac{5}{2},0),$dots

dots,$(0,-\frac{3}{2}),(0,-\frac{}{2}),(0,0),(0,\frac{}{2}),(0,\frac{3}{2}),(0,\frac{5}{2}),$dots

dots,$(0,-2),(0,-),(0,0),(0,),(0,2),(0,3),$dots

dots,$(-2,-2),(-,-),(0,0),(,),(2,2),(3,3),$dots