Question

To form an ellipse, what is the relationship between the base of the cone and the angle of the plane that intersects the cone?

Answer 1

The plane is at an angle that is neither parallel nor perpendicular to the base of the cone.

Explanation:

The plane doesn't need to be at an exact angle of 45 degrees. The most important thing is that the angle isn't parallel or perpendicular to the base of the cone, but it has to be non-zero without intersecting the base itself. It also only intersects one of the cones when looking at a double-cone.