Answer: x = −a.
- A x = −a
- B x = a
- C y = a
- D y = −a
Correct answer: A. x = −a
Explanation: For y² = 4ax the directrix is the vertical line x = −a.
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.