Circle Equation: Center (h,k)

This applet accompanies the Standard Form of the Equation of a Circle (Part 3) packet you received at the beginning of class today. Complete this activity and then answer the questions that appear below the applet.
Suppose P(x,y) = any point that lies on a circle with center (h,k) and radius r, where r > 0. Use what you've observed to write an equation that expresses the relationship among x, y, and r. (No need to square any binomial expressions!)