Adjoining the circles

The applet shows three circles adjoining together. In this applet, if the radius of the circle is changed by moving the center of the any one of the circles, the size of the other two circles change automatically. How it happens: Draw a triangle of the points A,B,& C. Find out the half the perimeter (ie) s= (a+b+c)/2. Draw the circles of radii s-a, s-b, s-c with the points A,B, & C as their center respectively.