# How do I define the function to be 0 at x=0?

Struggling first-year undergrad here... sorry if this question seems stupid.

I want to graph the 3d and contour plots of `f(x,y)=x*y*(x^2-y^2))/(x^2+y^2)`

.
Since the function is undefined at 0 I need to also define the function to be 0 at x=0.

Here's what I wrote

```
x, y = var('x y')
plot3d((x*y*(x^2-y^2))/(x^2+y^2), (-3, 3), (-3, 3))
```

```
contour_plot((x*y*(x^2-y^2))/(x^2+y^2), (-10, 10), (-10, 10), fill=0, labels=40)
```

The contour plot looks a bit funky, there's a big cross made by two lines at the origin which I suppose is because the function is undefined at 0.