[b]Slide points A, B, C, D to illustrate the result.[br][br]It is important to notice that lengths are always measured to the intersection of[br]the chords regardless of whether this intersection is inside or outside the circle.[/b][br][br]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.[br][br]Does this change the result?