Looking at the graph, we have a trigonometrical function. It can be a sine or cosine function.
Since it has the point (0, 0), we can use the sine function to model it.
Let's use the following equation to model it:

Where a is the amplitude, b is a horizontal compression factor, c is a horizontal shift and d is a vertical shift.
Looking at the graph, the amplitude goes from -3.33 to 3.33, therefore the value of a is 3.33.
The period of the function is equal to pi (3.14). We can use the following formula for the period, so we can calculate the value of b:

There is no horizontal or vertical shift, therefore c = 0 and d = 0.
So the function that represents this graph is:

Domain: All real numbers.
Range: [-3.33, 3.33].
Period: pi