Answer: 8.
- A 6
- B 8
- C 10
- D 5
Correct answer: B. 8
Explanation: The constant sum equals 2a = 2·4 = 8.
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.