The angle between the generator and the central axis of a double-napped cone is 40°. A plane intersects the central axis at an angle between 40° and 90°. Which conic section is formed?

The plane makes an angle greater than 40° with the cone’s axis, while the generator makes a 40° angle with the axis. Since the plane is steeper than the generator and is not parallel to it, it cuts one nappe in a closed curve: an ellipse.

AI-written and checked against the verified answer.