How do I find the directrix of the parabola whose equation is y=x232?

1 Answer
Oct 19, 2014

You have a parabola with vertex at (0,0) that is opening upward.

That means your directrix is horizontal.

To get the directrix, transfer x2's coefficient to the other side.
Equate the resulting coefficient of y to 4d, where d is the distance from the vertex to the directrix

y=x232
32y=x2

4d=32
d=8

Since the parabola is opening upward, the directrix is below the vertex.

y=hd

y=08

y=8