when we graphing a function, we can always start by picking points. Let's begin with an example of the simplest Trigonometric graph. `y = sin(x)`

`X`	`0`	`π/2`	`π`	`(3π)/2`	`2π`
`Y`	`0`	`1`	`0`	`-1`	`0`

You can see that the sine curve starts at 0, increases to 1, decrease to 0, further decrease to -1, and increases back to 0. Now, what if we pick more points to the left or right of the graph?

`X`	`0`	`-π/2`	`-`	`-(3π)/2`	`-2π`
`Y`	`0`	`-1`	`0`	`1`	`0`

Well, we find the graph just "repeats" itself. We call this function is periodic