Generating Conic Sections

This is the graph of Ax² + By² + Cx + Dy + Exy + F = 0. Use the sliders to adjust the values of A, B, C, D, E, and F. 1. What happens when E = 0? What shapes can you generate? 2. What other patterns can you detect? 3. What do you have to do to generate a circle? What has to be different in a circle and an ellipse?