Dandelin Spheres
Exploring Dandelin spheres of ellipse, hyperbola and parabola.
Geogebra 5 is required.
Use the slider to change the shape of the cone.
You may drag the points A, D or E to change the cross section of the cone.
For convenience, you may click the button to get suitable ellipse, hyperbola and parabola.
The two spheres touch the cone at two circles. They also touch the cross section at L and K respectively.