Answer: 20.
- A 16
- B 20
- C 36
- D 4
Correct answer: B. 20
Explanation: a=4, c=6, so b<sup>2</sup> = c<sup>2</sup> - a<sup>2</sup> = 36 - 16 = 20.
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.