Finding the Centre & Radius (Edexcel IAL Maths)

Spec point — 3.1

Finding the centre & radius

How do I find the centre and radius from the equation of a circle?

• A circle equation in a different form can always be rearranged into (x- a)²+ (y - b)²= r² form in order to find the centre and radius
• This will often involve completing the square

Exam Hint Make sure you are able to rearrange circle equations given in the general form $x^{2}+y^{2}+2fx+2gy+c=0$

Worked Example