This applet visualises the surface [math]z=y^2-4x^2[/math]. Shown in light blue is the horizontal plane at z = c, and the contour of the surface at z = c (in dark blue if c > 0 or red if c < 0). The contour is the intersection of the plane at z = c with the surface [math]z=y^2-4x^2.[/math] Use the slider to adjust c. As c changes, the contours trace out the surface [math]z=y^2-4x^2[/math]. Also shown is the cross section of the surface in the yz-plane, which has equation [math]z=y^2[/math], x = 0 (in darker blue) and the cross section of the surface in the xz-plane, which has equation [math]z=-4x^2[/math], y = 0.[br][br]The surface [math]z=y^2-4x^2[/math] is an example of a hyperbolic paraboloid.