+0

# Help with parabolas!

0
265
1

1. This isn't really a specific question, but in general, what would be ways to find the vertex of a parabola? (Assuming you know all the necessary information and whatnot)

2. How do you find the directrix of a parabola, and what would be its use?

Mar 6, 2019

#1
+1

It depends what form your equation is in.

If it is of the form

\((x-h)^2=4a(y-k)\)

Then the vertex is  (h,k)

the focal length is |a|

If a is positive then it is concave up, if a is negative then it is concave down.

The focus is (h,k+a)  the axis of symmetry is x=h   and the directrix is   y=k-a

The definition of a parabola is the locus of all points equidistant from a line called the directrix and a point called the focus.

Give the directrix and the focus you can determine the equation of the parabola using locus (which is a fun things to do when you get used to the method)

What would you use the directrix for ? ... not sure what this question is after but if you google it the answer may become clear :/

Mar 6, 2019