Exploring Angles Inside and Outside Circles
Move Point C or D to change the size of Arc1. Move Point E to change the location of the vertex of the angle or the size of Arc 2.
Step 1: Move point E to a point on the circle. Now you have an inscribed angle and you can once again see what we have already seen: the measure of the inscribed angle is half of its intercepted arc.
Now the question for today is: What can we say about angles inside and outside a circle?
Step 2: Move point E to the center of the circle. Point E is in the center if both the arc measures are equal. Angle E is a central angle and its measure equals the arc measure. Now move point E away from the center, but keep it inside the circle. Look at the relationship between the arcs and the angle. Move the points around to look at other angles inside the circle.
Step 3: Move point E outside the circle. Look at the relationship between the arcs and the angle. Move the points around to look at other angles outside the circle.