Congruent Chords Discovery

Interact with the following applet below for a few minutes, then answer the questions that follow. 1) Move the slider 2) Reset 3) Change the locations of the BIG POINTS each time before re-sliding the slider!
Questions: 1) Explain why the 2 circles shown are congruent. How do you know? 2) Notice how there are 3 congruent chords displayed. The red arc is said to be the arc "determined" (or "made") by these chords. What do you notice about the arc for all three chords?