When a function has values that repeat and repeat over and over (like Macbeth and his obsession with tomorrow and tomorrow and . . .), it's a periodic function.
Newsflash: all the trig functions are periodic. Let's see what sine and cosine look like when we slap 'em onto a graph.
Example 1
Graph y = -sin x. |
Example 2
Graph y = 0.5 sin x. |
Example 3
Graph y = -2 cos x. |
Example 4
Graph y = cos(½x). |
Example 5
Graph y = 2cos(2x). |