Pascal's Theorem
Two sets of points - A, B, C and A',B',C' are drawn on an ellipse.
[you can adjust the size and shape of the ellipse by dragging the purple dots]
The following sets of lines are drawn -
AB' and BA'
AC' and CA'
BC' and CB'
Each of these sets of lines intersect at a point.
Drag the points to persuade yourself that the three intersection points always lie on a straight line.
Can you explain why this is so?
What questions could/would you put to your students based on this applet?