## Visualization of graphs with Functions of Two Variables

Later we will have other explorations with this applet.
For now, make sure the applet is in input mode (you can get there
by using the **Show** menu).
Look at the plots for the
various function choices. Use the mouse to move the plot around in three dimensions.

You can also enter functions by hand.

Try the function *z = 2*sqrt(x^2 + y^2)*.

Use the **Show** menu to put the applet into **Partial
Derivatives** mode and put the pink dot (in the graph at the lower right)
at (0,0). This mode shows many things. What we're interested in at the
moment is the slices on the 3D plot. These are the traces of the graph in the
*xz* and *yz* planes. If you move the pink dot you get the traces
in planes parallel to the *xz* and *yz* planes, and the slopes of the
corresponding tangent lines to those trace curves.