A LevelMaths: PureOCRRevision Notes3. Coordinate Geometry3.2 Circles3.2.1 Equation of a Circle

Equation of a Circle (OCR A Level Maths: Pure)

Revision Note

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Author

Roger

Last updated

25 April 2023

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Equation of a Circle

What do I need to know about the equation of a circle?

A circle with centre (a, b) and radius r has the equation

${(x - a)}^{2} + {(y - b)}^{2} = r^{2}$

Eqn of Circle graph illustr, A Level & AS Level Pure Maths Revision Notes

You need to be able to find the centre and radius of a circle from its equation

Eqn of Circle Illustr 1, A Level & AS Level Pure Maths Revision Notes

You need to be able to find the equation of a circle given its centre and radius

Eqn of Circle Illustr 2, A Level & AS Level Pure Maths Revision Notes

Examiner Tip

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.

Worked example

Eqn of Circle Example, A Level & AS Level Pure Maths Revision Notes

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Previous:3.1.4 Modelling with Straight LinesNext:3.2.2 Finding the Centre & Radius

Author: Roger

Expertise: Maths

Roger's teaching experience stretches all the way back to 1992, and in that time he has taught students at all levels between Year 7 and university undergraduate. Having conducted and published postgraduate research into the mathematical theory behind quantum computing, he is more than confident in dealing with mathematics at any level the exam boards might throw at you.