1. A and B are the endpoints of a chord. You can find an infinite number of circles passing through A and B. The smallest has a radius of

2. The equation of a circle with its center at is:

3. If you havethreepoints of a circle you can calculate using the equation of #2.

4. If you know the equation of the circle you only have to plug in a x-value (or y-value) to calculate the missing coordinate. (r is a constant!)