What concept is dynamically being illustrated in the applet below?[br](Feel free to move the points and/or the circle anywhere you'd like.)
[b]Standard Form of the Equation of a Circle in the Coordinate Plane[br][/b][br]By the Pythagorean Theorem, [br][br][math]\left|x-h\right|^2+\left|y-k\right|^2=r^2[/math]. Since the absolute value of any quantity is never negative, we can write[br][br][math]\left(x-h\right)^2+\left(y-k\right)^2=r^2[/math]. [br][br]