Equation of a Circle

Think back to tranformations of parabolas, we used the point (h,k) to talk about our vertex.

We can use the same point to talk about the center of our circle.

We can write equations of circles from their graphs.

Locate the center of the circle. This usually marked with a dot

The other piece of information we need is the radius.

You can calculate the radius by counting the number of units from the center to any point on the circle.

 Now we can place our values into our equation

 $\left(x-\left(-2\right)\right)^2+\left(y-\left(2\right)\right)^2=\left(3\right)^2$  

Then simplify