[b]Slide points A, B, C, D to illustrate the result. It is important to notice that lengths are always measured to the intersection of the chords regardless of whether this intersection is inside or outside the circle.[/b] Circle Theorems [url]http://www.geogebratube.org/student/c89/m1462/yryy[/url]
You might want to look at the special cases when the points coincide and tangents to the circle are created. Does this change the result?