A periodic function is one that repeats over and over
again. There are three common trigonometric
ratios that can give periodic functions – sin, cos and tan. The
simplest graphs on a set of x-y axes are just sin(x), cos(x) and tan(x).
Notice that each cycle repeats over every 2p
interval, except for tan which repeats over every p interval. Sin(x) and cos(x) also have y values always between
1 and –1, whereas tan(x) can be anywhere from 
to 
(negative infinity to positive
infinity). Also note that the angles on the x-axis are in radians, not
degrees.
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Now of course, there are much more complicated functions than these. To be able to draw them, you must know the basic shapes shown here. From these basic curves you can then draw any of the more complicated curves.
