Proving that $f(x,y) = \frac{xy^2}{x^2 + y^2}$ with $f(0,0)=0$ is a continuous function using epsilon-delta. [duplicate]
Here is how you advance
$$ \frac{xy^2}{x^2+y^2} \leq \sqrt{x^2+y^2} < \epsilon=\delta.$$
Note: we used the inequality
$$ |a| \leq \sqrt{a^2+b^2}. $$