## Circles

In this tutorial you are shown how the equation of a circle is derived when you know the centre and radius.

Formulae to remember:

- (x – x
_{1})^{2}+ (y – y_{1})^{2}= r^{2}where the centre has coordinates (x_{1}, y_{1}) and radius = r^{2}

You will also be taken through this example.

Example:

- Find the equation of a circle with centre (4, -2) and radius 3.

You should be aware of the alternative form of the equation of a circle and how you can find the centre and radius.

In this video, we’ll look how to find the equation of a circle and tangent.