The explicit equation of the

angle bisector [angle]EAB (the one with the positive slope that corresponds to the straight line AF) is:

Prove that

angle bisectors at vertices A and B meet at the side CD.

Given two intersecting straight lines [l.sub.1] and [l.sub.2], one can fold their

angle bisectors a and a'.

The program allows students to construct points, segments, circles, parallels, perpendiculars,

angle bisectors, and extensions of line segments.

Because the solution of the task requires some knowledge of the material learned in plane geometry as part of the high-school program of studies (including the ones presented in the Australian schools), when this problem is presented to students, it should be presented only after they have studied the circle and special segments in the triangle (altitudes,

angle bisectors, etc.).

The definition of the incenter of a triangle is a center of triangle's inscribing circle, and be constructed as a point where three

angle bisectors intersect.