### Introduction

A circle is one of the most familiar geometrical figures and has been around a long time! In this brief Section we discuss the basic coordinate geometry of a circle - in particular the basic equation representing a circle in terms of its centre and radius.

#### Prerequisites

- understand what is meant by a function and be able to use functional notation
- be able to plot graphs of functions

#### Learning Outcomes

- obtain the equation of any given circle
- obtain the centre and radius of a circle from its equation

#### Contents

1 Equations for circles in the $Oxy$ plane1.1 Circles with centre at the origin

1.2 Circles and functions

2 Annuli between circles