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An interactive three dimensional plot of a curved surface shown in gray above a set of axes labeled
\(x\text{,}\) \(y\text{,}\) and
\(z\text{.}\) The gray surface decreases as you move away from from a maximum near the z-axis. A slider at the top of the figure changes the direction of an arrow shown below the surface on the xy-plane in red. A gray segment is drawn from the beginning point of the red arrow, parallel to the z-axis, up to the surface. A point where the gray segment intersects the surface his highlighted. A blue plane is shown extending from the red arrow parallel to the z-axis, through the surface. The curve along the surface that is above the red segment and is the intersection between the curved surface and the blue plane is drawn in blue. As the direction of the red arrow changes the profile of the blue curve changes according to the shape of the surface in the given direction.