# Thread: Radii and centre of a circle.

1. ## Radii and centre of a circle.

A level Maths.
Induction.
Write down the centre and radius of the given circle x^2+y^2=4
I have not come across quadratic equations for radii

2. This question is in the wrong forum, incidentally. You should post this question in either geometry or algebra.

The general equation for a circle of radius $r$ centered at the point $(a,b)$ is $(x-a)^{2}+(y-b)^{2}=r^{2}.$ From this, can you read off the coordinates of the center, and the radius?