How do you find the equation of a circle?

The equation of a circle is given in the form (x-a)2 + (y-b)2 = r2, in which the centre of the circle is (a,b) and the radius of the circle is 'r'. If you can figure out or are given the co-ordinates of the centre of the circle and the radius then these values can be plugged into the above equation to find the answer. Occasionally, you may not be given these values and will instead be given the equation in the form x2+y2+cx+dx=k, in which c, d and k are constants. In this case, you can "complete the square" for x and y in order to rearrange the equation into the model above. This will allow you to then also figure out the centre of the circle and the radius should you need it.

ZK
Answered by Zeeshan K. Maths tutor

3703 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Make x the subject of the formula 4(2x-y) = 3ax - 5


Find the stationary points of y = x^3 -3x^2 - 9x +5


How do you find the maximum and minimum value of a quadratic function with no use of calculus?


How to apply the quadratic equation


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning