Answer: A double-napped right circular cone.
- A A right circular cylinder of fixed radius
- B A double-napped right circular cone
- C A sphere centred at the origin
- D A flat circular disc lying in a plane
Correct answer: B. A double-napped right circular cone
Explanation: Conic sections (circle, parabola, ellipse, hyperbola) are obtained by intersecting a plane with a double-napped right circular cone at different angles.
All four conics form a single family distinguished only by eccentricity: a circle is the most "closed" (e=0), an ellipse is an elongated closed curve, a parabola is the borderline open curve (e=1), and a hyperbola has two separate open branches (e>1).
Concept context
Study circles, parabolas, ellipses, and hyperbolas as curves formed by intersecting a plane with a double cone, with their standard equations and key properties.