As you can see from the extended sine and cosine graphs, each curve repeats itself regularly. This trait is called "periodicity", because there is a "period" over which the curve repeats itself over and over. The length of the period for the sine and cosine curves is clearly 2π: "once around" a circle. Also, each of sine and cosine vary back and forth between –1 and +1. The curves go one unit above and below their midlines (here, the x-axis). This value of "1" is called the "amplitude".

When you graph, don't try to plot loads of points. Note that the cosine is at y = 1 when x = 0 and 2π; at y = 0 for x = π/2 and 3π/2, and at y = –1 for x = π. Plot these five "interesting" points, and then fill in the curve.