The function in this exercise is .  The purpose of this exercise is to show that for this function,  as  along any line , but  as along the parabola .  This ill-behaved function (around ) caused Plot 3D some difficulties.  The plot below was created in Cartesian mode with the viewer angle with the x-axis set at 60 degrees and the viewer angle with the z-axis set at 40 degrees.  Both the top and bottom surface are colored white to mask some shading problems.

A closer look at the figure at the top of page 945 suggests that a coordinate system other than Cartesian coordinates was used to create that figure.  The plot below is of the same surface, but sketched in cylindrical coordinates, so that the function becomes . This figure looks a lot more like the one at the top of page 945.