Pre Cal
posted by Marie .
write the equations of the parabola, the directrix, and the axis of symmetry.
vertex: (4,2)
focus: (4,6)
if someone could explain how to do this problem then that would be great! thanks in advance!
Formats to help you find the equation for a parabola:
(x  h)^2 = 4p(y  k)
Vertex = (h, k)
Focus = (h, k + p)
Directrix: y = k  p
You are given the vertex (4,2) and the focus (4,6).
Since we know k, which is 2, we can figure out p. Format = (h, k + p) for focus. Therefore, p = 4.
I'll set this up and let you take it from there:
[x  (4)]^2 = 4(4)(y  2)
The axis of symmetry is: x = 4 (vertex xvalue).
I hope this will help.
good post. mathguru, if you would like to join us here at jiskha as a volunteer teacher, email me at
bobpursley@gmail.com
it did. thanks so much!
Thanks Bob! Just happy to help. :)

x^2=24y