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## Homework Statement

Hi there. Well, I've got some doubts on the partial derivatives for the next function:

[tex]f(x,y)=sg\{(y-x^2)(y-2x^2)\}[/tex] Where sg is the sign function.

So, what I got is:

[tex]f(x,y)=f(x)=\begin{Bmatrix}{ 1}&\mbox{ if }& (y-x^2)(y-2x^2)>0\\0 & \mbox{if}& (y-x^2)(y-2x^2)=0\\-1 & \mbox{if}& (y-x^2)(y-2x^2)<0\end{matrix}[/tex]

How should I get the partial derivatives? I'm sure that for the zero I must use the definition. But in the other cases should I?

Bye, and thanks.

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