Question

What is the equation of the directrix for the conic section shown below?
y^2=-36x
x=4
x=9
y=-6
y=9

I think it is x=4.

Answer 1

I need help

Answer 2

you got yourself a parabola with vertex at the origin \((0,0)\)

Answer 3

do you know if it opens left, right, up or down?

Answer 4

Left. @satellite73

Answer 5

you need to know that first to find the directrix
right, it opens to the left

Answer 6

this looks just like \[y^2=4px\] what is \(p\)?

Answer 7

p=1?

Answer 8

\[4p=-36\\
p=?\]

Answer 9

oh! -9

Answer 10

My bad, I am sorry.

Answer 11

yeah and the fact that you know it has vertex at \((0,0)\) and opens to the left tell you that the directrix is a vertical line 9 units to the right of the vertex

Answer 12

@satellite73 y=9 then, since you said vertical?

Answer 13

since i said it was vertical it is not y equals anything
that would be horizontal

Answer 14

OH. Yeah... (duh) I am like half brain dead, I've been doing finals all day. SO, its x=9, then, right?

Answer 15

yup

Answer 16

@satellite73 thank you muches

Answer 17

welcome muchos