Isosceles Triangle: Surprising Theorem!
Creation of this applet was inspired by a problem from the 2006 Irish Mathematical Olympiad that was posted on one of Cut-The-Knot's Wiki Pages.
If a point P lies on one leg of an isosceles triangle with vertex angle A and leg length k so that 0 < AP < k, and if another point Q lies on the other leg of this isosceles triangle so that AQ = k - AP, then the circumcircle of triangle APQ will ALWAYS pass through the CIRCUMCENTER of the isosceles triangle.