To find the equation of a circle when you know the radius and centre, use the formula (x a) 2 + (y b) 2 = r 2, where (a, b) represents the centre of the circle, and r is the radius.

The formula for the area of the circle is 𝑨 = π𝒓². To work out the area of a circle: Find the value of the radius. If the diameter is given, this must be halved.