Circles
Key Facts
You must learn the following:
- The equation of a circle with centre and radius is given by
- If the equation is given in expanded form, eg. , then it is necessary to complete the square before identifying the centre and radius:

Test Yourself - Equation of a Circle
Relevant Circle Theorems


![A chord will be [b]perpendicularly bisected [/b]by a specific radius.](https://www.geogebra.org/resource/cPLWiDdw/f4M6NdjjEUGFxolh/material-cPLWiDdw.png)