Let Using polar coordinates, prove that and that does not exist. Show that g(x, y) = cos 2 and observe that cos can

Let  Using polar coordinates, prove that  and that  does not exist. Show that g(x, y) = cos²θ and observe that cos θ can take on any value between −1 and 1 as (x, y) → (0, 0).

f(x,y) = x/(x + y) and g(x, y) = x/(x + y).