G.GCI.2 Angle Formed by 2 Chords
In the applet below, the gray angle is said to be an angle formed by 2 chords of a circle.  
Interact with this applet for a few minutes.  As you do, be sure to change the locations of the BIG POINTS each time before re-sliding the slider!  
What are the relationships between the inscribed angles, arcs, and angles formed by intersecting chords?