Unit circle Cosine wave

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As you can see from the extended sine and cosine graphs, each curve repeats itself with unbroken regularity. This distinctive trait is called "periodicity", because there is a consistent "period" over which the curve repeats itself again and again. The length of the period for the sine and cosine curves is clearly 2π: one complete circle around. Also, each of sine and cosine varies back and forth between –1 and +1 with equal ease. The curves rise one unit above and fall one unit below their midlines (here, the x-axis). This value of "1" is called the "amplitude". When you graph, try to plot just a few key points instead of lots of scattered ones. 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 first, then fill in the curve with a smooth line.