Étudier l’existence des limites suivantes :
1
\(\mathrm{lim}_{\begin{smallmatrix}(x,y)\to (0,0)\\ x+y\ne 0\end{smallmatrix}} \frac{x^2y}{x+y}\)
2
\(\mathrm{lim}_{\begin{smallmatrix}(x,y,z)\to (0,0,0)\\2x^3+yz^2 \ne 0\end{smallmatrix}} \frac{xyz+z^3}{2x^3+yz^2}\)
3
\(\mathrm{lim}_{\begin{smallmatrix}(x,y)\to (0,0)\\(x,y)\ne (0,0)\end{smallmatrix}} \frac{|x|+|y|}{x^2+y^2}\)
4
\(\mathrm{lim}_{\begin{smallmatrix}(x,y)\to (0,0)\\ x \ne \pm y\end{smallmatrix}} \frac{x^4y}{x^2-y^2}\)
5
\(\mathrm{lim}_{\begin{smallmatrix}(x,y,z)\to (0,0,0)\\(x,y,z) \ne (0,0,0)\end{smallmatrix}} \frac{xy+yz}{x^2+2y^2+3z^2}\)