Intersection of secants in a circle

Topic:
Circle
Theorem: If two lines intersect at point and intersect a circle at points and respectively, then = Drag the blue points to the following configurations and see the products and . In each case, see why the corresponding angles in the blue and brown triangles are congruent.
  • M - outside the circle;
  • M - inside the circle;
  • M - on the circle;
  • P=Q and R different than S;
  • P=Q and R=S