Use the Show menu to put the applet in input mode.
Choose the input x^2 - y^2 + 3 from the drop-down list and click the 'plot' button.
Use the Show menu to put the applet in level curves mode.
Check the 'show all contour lines' box.
Move the slider on the bottom left
back and forth and watch the yellow contour move.
Explain what is happening as the slider goes through z = 3.
Now use the
Show menu to put the applet back in in input mode and
choose input x^2+y^2 + 1.
Before going back to level curves mode predict what the level curves will look like.
What will they look like around the minimum at (x,y) = (0,0)?