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Reviewed CSCA Mathematics question · Easy

A parabola has its vertex at the origin and its focus at (2, 0). What is the equation of its directrix?

  1. x = -2
  2. x = 2
  3. y = -2
  4. y = 2
Show the answer and explanation

Correct answer

A. x = -2

Principle or equation

For a parabola with vertex at origin and focus (p,0), the directrix is x = -p.

Why this answer is correct

The focus is (2,0), so p = 2. The directrix is the vertical line x = -2.

Example

If focus is (3,0), directrix is x = -3.

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