Incircle

Find the radius of the incircle of the triangle.

To construct the incircle of ΔABC, we need the center of the circle and a pass-through point.

Having constructed K, the incircle of the quadrilateral can be easily constructed since it is tangent to BA and BC.

For example, in Figure 4.2a only two edges of the polygon are tangent to the incircle. The other four edges do not even touch the incircle, but their extensions, shown by dotted lines, are tangent to the incircle.