Hello everyone

$\displaystyle f: \mathbb{R}^2 \to \mathbb{R}, \ \ \ x,y \in \mathbb{R} $

$\displaystyle f(x,y) := \begin{cases} \frac{xy}{x^2+y^2}, & \mbox{if } (x,y) \not= (0,0) \\ 0, & \mbox{if } (x,y) = (0,0) \end{cases}$

Show that f is not continuous in (0, 0)

I really do not know how to solve that.

Thanks for your time.

Rapha