What do I need to know about the equation of a circle?
- A circle with centre (a, b) and radius r has the equation
- You need to be able to find the centre and radius of a circle from its equation
- You need to be able to find the equation of a circle given its centre and radius
- Remember that the numbers in the brackets have the opposite signs to the coordinates of the centre.
- Don't forget to take the square root of the right-hand side of the equation when finding the radius.