Find the standard form of the equation of the parabola with a focus at (0, -9) and a directrix y = 9.

answer choices:
y = -1/9^2

y^2 = -36x

y = -1/36^2

y^2 = -9x

Question

Find the standard form of the equation of the parabola with a focus at (0, -9) and a directrix y = 9.

answer choices:
y = -1/9^2

 y^2 = -36x

 y = -1/36^2

 y^2 = -9x

jdoe0001 · Answer

where do you think is the origin at ?

anonymous · Answer

Is the origin also the vertex?

jdoe0001 · Answer

|dw:1383170844831:dw|

so yes, is at the origin, notice that you can just plug those values in a "focus form" of a parabola like, the parabola is going downwards, so the $\large \bf (x-h)^2=-4p(y-k)$

(h, k) = vertex coordinates
p = distance from the vertex to the focus or directrix, since the directrix and focus are equidistant from the vertex

anonymous · Answer

Okay so, I would no be able to fill in the values. 

(x-0)^2=-4(9)(y-0)

x^2=-36y

jdoe0001 · Answer

$\bf x^2=-36y\implies -\cfrac{x^2}{36}=y$    yeap

anonymous · Answer

Awesome! Thank you so much for helping!

~clear skies

jdoe0001 · Answer

yw