Question

What is the directrix of the parabola given by the equation x = 7y2 + 126y + 559?

Answer 1

directrix is line perpendicular to axis of symmetry right?

Answer 2

Yep!

Answer 3

And that should be 7y^2 by the way.

Answer 4

lol yh i figured

Answer 5

crap i cant remember how to do these probs, give me a minute or two

Answer 6

do we just solve for y values intersecting the y axis

Answer 7

wait so shouldnt question be what is equation of parabola cause u already have equation of directrix

Answer 8

hey wher'd u go?

Answer 9

Sorry, my internet quit for a second. And no, that's not the equation of the directrix, thats the equation of the parabola.

Answer 10

for a second i thought i was talking to my self :P

Answer 11

Haha, no no. I wouldn't do that to you :)

Answer 12

umm but equation of parabola cannot be in for x=ay^2+by +c

Answer 13

can u check ur question again

Answer 14

It's...well, that is what the question asks, but it's...

Answer 15

lol sorry i cant help u i dont know how to solve it this way

Answer 16

I don't know how to explain this without showing you. I'm doing a section of conics in my online class and you CAN have a parabola with x = blahblahblah, but I just need it to be written in general form

Answer 17

repost it and some smart kid might be able to do it

Answer 18

like a(x - h)^2 + h

Answer 19

oh ok

Answer 20

hold up

Answer 21

Haha, okay

Answer 22

crap u are right so sorry, i think give me some time

Answer 23

i think answer is 1/28

Answer 24

in x = 7y2 + 126y + 559 the a value is = 1/4p hence it equals 1/28

Answer 25

if thats not the answer i dont know it

Answer 26

Oh my gosh, you're brilliant :) Thank you!

Answer 27

aww shuks, thankx =)

Answer 28

Oh wait...is it -8 and 1/28 or -7 and 27/28?

Answer 29

no its p=1/28

Answer 30

the line travelling along the x axis

Answer 31

hey u there i wanna know if its right?

Answer 32

Well, I won't know if it's right until I turn it in, but i don't want to turn it in if it's not right.
It'ls a big catch 22.

Answer 33

so lonely);

Answer 34

whats the question? the one at the very top?

Answer 35

yh

Answer 36

The 28 part makes sense, that's part of the answer choices, but I need to know the rest.

Answer 37

What is the directrix of the parabola given by the equation x = 7y2 + 126y + 559?

Answer 38

lol im only in grade 11 so most of this beyond me

Answer 39

Lol, I'm in grade 11 too :)

Answer 40

No worries though, I'm not understanding this question any better than you are and I'm looking at the course material right now!

Answer 41

lol i never learnt this, i looked it up once for a contest math problem but never did it

Answer 42

man my school sux i learn nothin

Answer 43

im trying to find the formula for the directrix. google is failing me lol =/

Answer 44

Again, no worries. My school is so terrible, I'm transferring to a new school in a whole 'nother city and I'm not moving there either. I'll just be driving 30 minutes each way.

Answer 45

wikipedia it

Answer 46

i would start by completing the square though, most likely that would be the first step to figuring out the directrix.

Answer 47

Oh! Joe, I can help you with that one. The directrix is x = h - c

Answer 48

Hahd figured out c, but now we need h

Answer 49

lets complete the square first just to make the equation look nice:
\[7y^2+126y+559 = 7(y^2+18y+81)+559-567 = 7(y+9)^2-8\]

Answer 50

so now we have:
\[x = 7(y+9)^2-8 \iff x+8 = 7(y+9)^2 \iff \frac{1}{7}(x+8) = (y+9)^2\]

Answer 51

oh my...

Answer 52

Holy cow! That's super close to the form we need to get it in!

Answer 53

according to some websites, the standard form of a parabola is:
\[(y-k)^2 = 4p(x-h)\]

Answer 54

the 4p is going to equal that fraction we have, so:
\[4p = \frac{1}{7} \iff p = \frac{1}{28}\]

The directrix is going to be:
\[x = -p+h = -\frac{1}{28}+ (-8) = -\frac{225}{28} \]

Answer 55

<3

Answer 56

You're awesome. Thanks so much!

Answer 57

man my computer died

Answer 58

i had it too 0;

Answer 59

i did the right thing calling joemath

Answer 60

You called him?

Answer 61

its hard to remember all these parabola formulas >.<

Answer 62

yh

Answer 63

he's helped me before

Answer 64

plus he's in uni so its like help from an older friend

Answer 65

How do you call someone on here? Or do you know him personally? And YES. It is extremely difficult. The amount of formulas there are for arithmetic and geometric sequences alone is enough to kill you.

Answer 66

lol when u see them answering someones answer spam that wall

Answer 67

Thanks to both of you though. You were incredibly helpful.

Answer 68

meh joemath is awesome

Answer 69

Hahahaha, I will certainly keep that in mind for future references :)

Answer 70

Yes he is!

Answer 71

psh im awesome too just at stuff i know bye

Answer 72

Yes, you were definitely awesome too :) Farewell!

Answer 73

hahd is very awesome :)

Answer 74

LOL thnkx

Answer 75

the good thing is i actually learned stuff so i feel good

Answer 76

thats why i stay around lol. sometimes you learn a new technique to solve something, or maybe you learn to solve something you couldnt before.