Limit of multivariable $\frac{x^2+y^2}{ x^4+y^4}$ Find the limit
$$\lim_{(x, y) \to (0,0)} \frac {x^2+y^2 }{x^4+y^4 }$$ 
This limit does not exists since when convert it into polar we get $\frac {1 }{ r^2 (1-2 \sin^2 \theta   \cos^2 \theta)}$  which is one over zero right?

plugging $$x=\frac{1}{\sqrt{n}},y=\frac{1}{n^2}$$ in the term above we get
$${\frac { \left( n+1 \right)  \left( {n}^{2}-n+1 \right) {n}^{4}}{
 \left( {n}^{2}+1 \right)  \left( {n}^{4}-{n}^{2}+1 \right) }}
$$ and the limit is $$+\infty$$
