f(x,y) = x^2 + y^2 - 3 abs(xy)

What does the vertical cross section of the surface along a diagonal through the origin (ie. the plane y = x = t) look like?

I graphed this in Scientific Workplace and got a paraboloid, but I don't see a paraboliod in the graph of the function, can someone please help me to see how to get this?

Thanks