Answer: 2a, a constant.
- A 2a, a constant
- B a, the semi-axis
- C b, the semi-axis
- D the eccentricity e
Correct answer: A. 2a, a constant
Explanation: This defining property gives a constant sum equal to 2a, the length of the major axis.
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.