1. Introduction
Here we give an interesting property of isosceles triangles. It is known that if a and b are two given line segments, then their third proportional line segment c can be constructed geometrically; see [2, VI.11]. We can more easily construct the third proportional line segment by using the simple geometric property of the isosceles triangles. Two points A and B are inverse points with respect to the inversion circle with center O and radius r, ifOA· OB = r2; see [3]. We can construct the inverse point with respect to a circle by using the same property of the isosceles triangle