Question

How do you find the center and radius of the circle `(x - 3) ^2 + (y + 1) ^2 = 9`?

Answer 1

Center `(3, -1)`
`radius = 3`

Explanation:

The centre-radius form of a circle is `(x - h)^2 + (y - k)^2 = r^2` with the centre being `(h, k)` and `r` as the radius.

Given this, we would know that the center of the circle is `(3,-1)` and the radius is 3.

Luckily we are given the centre-radius form so we can easily get/compute for what was asked. However, if we are given the standard form of a circle, we should first do completing the square to transform it into its center-radius form.