-Radius is the distance from the center to a point on the circle
- When you are getting your center from the equation, you will take the opposite of what is in the parentheses
-When finding your radius from an equation, you will square root the number that the equation is equal to.
-(x-h)^2+(y-k)^2=r^2
 where the center is (h,k) and radius is r
- In order to write an equation of a circle, you MUST have the center and the radius

-center is going to be in the MIDDLE of the diameter
- If you know the endpoints of the diameter, you will use the midpoint formula
 to find the center
- To find the radius, use the distance formula from the center to one of the endpoints of the diameter

-Once you have the center and the radius, you can plug them into the equation.
 -To determine if a point is ON the circle, you will find the DISTANCE between the point that is in question and the center. If the distance is equal to the radius, then the point DOES fall on the circle. If the distance does NOT equal the radius, then point DOES NOT fall on the circle.