Instructions:
1. Create two sliders, one for height and one for length. Set them to a range of 1-10. Move one of the sliders to a different amount than the other to help differentiate the circles.
2. Create one "circle with radius" and name the quantity for the radius as Length. This will affect the length of the ellipse. Do the same for the "Height" quantity. Put the center of both circles in the same spot. One circle should be bigger than the other, and this will be called the outermost circle. The latter will be called the inner circle.
3. Create a line from the center point to the outermost layer of circles and add a point at the intersection. Create another point where it intersects with the inner circle.
4. Now construct parallel lines. The point on the outermost circle should be used to construct a parallel line to the y-axis. The next parallel line should be constructed from the point on the inner circle and should be parallel to the x-axis.
5. Create a point for the area of intersection of the two parallel lines.
6. Add trace for that point and feel free to move or animate the point on the outermost circle.
7. You should have an adjustable ellipse!