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:
![Image](https://www.geogebra.org/resource/leDwV24Y/rZWkG5q3FPLXYJEP/material-leDwV24Y.png)
Test Yourself - Equation of a Circle
Relevant Circle Theorems
![Relevant Circle Theorems](https://www.geogebra.org/resource/O4U3UTpO/KqjrphoyeZNjDFRe/material-O4U3UTpO.png)
![The length from a point along a tangent can form a right-angled triangle.](https://www.geogebra.org/resource/SF5VTqWk/WqBGTPFtcCEdteI1/material-SF5VTqWk.png)
![A chord will be [b]perpendicularly bisected [/b]by a specific radius.](https://www.geogebra.org/resource/cPLWiDdw/f4M6NdjjEUGFxolh/material-cPLWiDdw.png)