An interesting phenomenon occurs when simple curves are displayed as the ``envelope'' of a more complicated function. Such things happen in practice when low-frequency waves (say, frequencies in the audible range for the human ear) ride carrier waves broadcast from a radio station.
The following example shows the curve y = 4 sin x + 3 cos 3x ``riding'' on top of the carrier y = sin 30x.
Plot 2D + Rectangular
4 sin x + 3 cos 3x,(4 sin x + 3 cos 3x)sin 30x
dtbpF3in2.0003in0pt
You can generate this plot by plotting 4 sin x + 3 cos 3x, and then dragging the expression (4 sin x + 3 cos 3x)sin 30x into the frame.