Secants Intersecting Outside the Circle
by Sofia Arcoy
Drag Points D, B, and F to observe the relationship of Arcs FB and EC to Angle CDE.
In the figure above, Secants BD and FD intersect at point D, and they form Angle CDE. As you may have observed, the measure of Angle CDE is equal to one half the positive difference of Arcs BF and CE.