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} \\ \text{where the centre }= (x_1, y_1) \text{ and radius }= r

You will also be taken through this example.

Example:

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