There are different ways to do it.

Cartesian method (y = f(x))

You will need two functions because of the limitations of the cartesian coordinate system, obtained by rearranging the circle equation in terms of x:

and

Polar method

This one is simple.. , since the radius of a circle is constant.

Parametric method

Use the trigonometric functions and .

You can change the type of graphing method in the setup menu of your TI.