- Josh Berberian
Start by checking out this video on how to create an ellipse by folding paper.
Now explore the applet below. Drag the yellow control point around the circle. Why is the yellow segment congruent to the blue segment? What is always true about the sum of the lengths of the red segment and the yellow segment? What is always true about the sum of the lengths of the red segment and the blue segment? Drag blue control point F2. What changes? What remains the same? Under what circumstances does the difference of the lengths of red segment and the blue segment remain constant? Select the Show Locus button and drag F2. What does the eccentricity appear to measure?