Make a GeoGebra file such as below.

Definition: A circle is the set of points equidistant from a point C(h,v) called the center. The fixed distance r from the center to any point on the circle is called the radius. The standard equation of a circle with center C(h,v) and radius r is as follows: [math](x - h)^2 + (y - v)^2 = r^2 [/math]