Question

Where is the directrix of a parabola?

Answer 1

The directrix of a parabola:

• The directrix of a parabola is dependent on the opening of a parabola.

• The directrix of a parabola is a perpendicular line to the line joined by the vertex and focus.
• The directrix never touch the parabola.
• If the parabola opens upward or downward direction, the directrix will be a horizontal line $y=c$.
• If the parabola opens left or right direction, the directrix will be a vertical line $x=a$.
• The distance between vertex and focus is the same as the distance between directrix and vertex. But focus and directrix lie in opposite directions.