 [Not to be turned in] In class, we talked about how to use $x$ and $y$traces to understand the graph of a function $f\colon\R^2\to\R$ and used the example $f(x,y) = x^2 + y^2$, whose graph is a paraboloid.
Apply similar techniques to the following functions, to see if you can get a sense of what they look like
 $f(x,y) = x^2  y^2$
 $f(x,y) = x^3  y^2$
 $f(x,y) = xy$
 Do the next WeBWorK assignment.

