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#1
So yeah, I have a problem like this.

What is the equation of a parabola with directrix y = -x + 2 and focus (3,3)

It's not vertical or horizontal, so it may be a little tricky. Whoever helps me out the most gets something special .
#2
The what in the what now...?!
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#6
I just found that seriously confusing...im pretty sure i have had that in a maths class but that just freaked me out and made me think how much i really learned

EDIT: Actually i think it was in the test i had just now...i failed it
Guitars:
-Schecter C-7 Hellraiser
-Ibanez MTM2
Amplifiers and Cabinets:
-Peavey StudioPro
-Randall RH50T Head
-Behringer 4x12 cab
Pedals:
-Ibanez WD-7 Wah
-Boss SD-1
-MXR 10 Band Equalizer

7-String guitars are badass!
#7
Quote by LiquidTension99
So yeah, I have a problem like this.

What is the equation of a parabola with directrix y = -x + 2 and focus (3,3)

It's not vertical or horizontal, so it may be a little tricky. Whoever helps me out the most gets something special .


... What the?
#9
Quote by RPGoof
I've heard of a parabola... WTF is all this other crap??? Don't you need something to be squared for a parabola?


Yep. It's usually based around y=x^2, but it's usually more complicated than that.
#11
Quote by LiquidTension99
So yeah, I have a problem like this.

What is the equation of a parabola with directrix y = -x + 2 and focus (3,3)

It's not vertical or horizontal, so it may be a little tricky. Whoever helps me out the most gets something special .

i think you substitute in the values from the co-ordinates into the equation......... i think
#12
answer me this. give me one day to day situation where you would ever need that. (this thread doesn't count.)
#13
^Thats hardly the point...you think his teacher would accept that 'apology'?

Quote by BIGSTEVERIGHTS
i think you substitute in the values from the co-ordinates into the equation......... i think

I actually got that far myself but that seems so confusing to me it blows my brain
Guitars:
-Schecter C-7 Hellraiser
-Ibanez MTM2
Amplifiers and Cabinets:
-Peavey StudioPro
-Randall RH50T Head
-Behringer 4x12 cab
Pedals:
-Ibanez WD-7 Wah
-Boss SD-1
-MXR 10 Band Equalizer

7-String guitars are badass!
#14
Hmm....did that in my first semester in uni, give me a few minutes, i'll see if i can work it out! Altho i always found it tricky when they were rotated...............
#18
Quote by bendystraw
answer me this. give me one day to day situation where you would ever need that. (this thread doesn't count.)

YES! 99% of the crap they teach you at school WON'T BE USED unless you are a MATH TEACHER
I'm learning tangents and **** and it's good for estimating the height of crap... Some stuff you might need to know for architecture or something though
#21
Quote by RPGoof
YES! 99% of the crap they teach you at school WON'T BE USED unless you are a MATH TEACHER
I'm learning tangents and **** and it's good for estimating the height of crap... Some stuff you might need to know for architecture or something though

I just had a test in it...i failed. Got total black out and the stuff was so ****ing complex written. I was in a fever and felt sick so i just said "meh whatever man! I will try again in 2 weeks when the failed people do the test again"
Guitars:
-Schecter C-7 Hellraiser
-Ibanez MTM2
Amplifiers and Cabinets:
-Peavey StudioPro
-Randall RH50T Head
-Behringer 4x12 cab
Pedals:
-Ibanez WD-7 Wah
-Boss SD-1
-MXR 10 Band Equalizer

7-String guitars are badass!
#23
the directrix is a line such that the distance from any point of the parabola to the focus is equal to the (perpendicular) distance from the point to the directrix. Does that do it?
TheBurningFish wrote:
I don't mean to generalise but I don't believe the average Coldplay fan is a massive musical theory nut.


FS/FT: Cort SP1 Stratocaster
Zoom GFX5 fx processor
Washburn BD40 amp
$100 each OBO
#24
Quote by DarkTom666
That's not a parabola..

A parabola is y = ax² + bx + c, you only have y = bx + c, so it's a straight line with x = 1 and goes through (3,3)



Well it's the y = ax² + bx + c that i'm looking for. I have y = bx + c for the directix, which is a line that does not go through 3,3.
#25
Quote by chubbychunks
Erm, that's not a parabola. That's a straight line.


This.
Quote by Trefellin
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LastFM
#26
Quote by LiquidTension99
Why?

Why should it be a parabola? The highest power is x^1

Anyway, this line can't exist. It's got a negative gradient, which apparently goes through (0,2) and (3,3).
#27
Quote by chubbychunks
Why should it be a parabola? The highest power is x^1

Anyway, this line can't exist. It's got a negative gradient, which apparently goes through (0,2) and (3,3).


A directix and a parabola are two different things. It was the directix that had a non quadratic equation.
tl;dr : IM BETTER THAN YOU
#28
Quote by chubbychunks
Why should it be a parabola? The highest power is x^1

Anyway, this line can't exist. It's got a negative gradient, which apparently goes through (0,2) and (3,3).



How do we know that it's highest power is x^1, the only power i've given you is that of the directrix, which is a line. The directrix does not go through (3,3), in fact, nothing important goes through (3,3) as far as I can tell.
#29
Oh, I see now. Sorry, misread. So you're looking for some crazy curve which kinda revolves around (3,3)?
#30
You n00bs! its a coinc, its focus is (3,3), the parabola doesnt go through it, the directrix is just a line which in a tangent to the stationary point of the parabola! Its all about the eccentricity dudes!
Im working on it btw
#31
Quote by chubbychunks
Why should it be a parabola? The highest power is x^1

Anyway, this line can't exist. It's got a negative gradient, which apparently goes through (0,2) and (3,3).
how many more people are going to post this? The focus is at (3,3) and the equation y = -x + 2 is the directrix. They are separate from each other; you dont plug in the (3,3) to the equation. And the directrix is NOT the parabola. Find the distance from the directrix to the focus and that will be your distance from the focus to any point on the parabola. You can then find the EQ of the parabola.
TheBurningFish wrote:
I don't mean to generalise but I don't believe the average Coldplay fan is a massive musical theory nut.


FS/FT: Cort SP1 Stratocaster
Zoom GFX5 fx processor
Washburn BD40 amp
$100 each OBO
#32
This is one of the things that bug me the most about the Pit.

People who can't be bothered to think occasionally and want to rely on others to do their (simple) homework for them.

And don't give me this "the teacher didn't explain it" bullcrap either.

- Pay attention more in class instead of chatting to friends
- If you don't get it, ASK THE TEACHER.

/rant

"flame" me all you want (with amazing insults such as "douche" and "n00b" ) but you know it's true.

You're not going to be able to ask anyone in a exam are you, so why do it now?
#33
Quote by chubbychunks
Oh, I see now. Sorry, misread. So you're looking for some crazy curve which kinda revolves around (3,3)?



Correct
#34
Quote by Kinks>Stones
This is one of the things that bug me the most about the Pit.

People who can't be bothered to think occasionally and want to rely on others to do their (simple) homework for them.

And don't give me this "the teacher didn't explain it" bullcrap either.

- Pay attention more in class instead of chatting to friends
- If you don't get it, ASK THE TEACHER.

/rant

"flame" me all you want (with amazing insults such as "douche" and "n00b" ) but you know it's true.

You're not going to be able to ask anyone in a exam are you, so why do it now?



Well, now that you bring it up, this is extra credit for the upcoming test. This is a highschool algebra 2 class, and a problem like this is not in the textbook. Because it's for extra credit, the teacher would not help us with it and wanted us to figured it out another way. And despite the fact that you may find it simple, I do not, so perhaps you should go be far superior somewhere else, dip****.
#36
Quote by LiquidTension99
And despite the fact that you may find it simple, I do not,


Simple?!

I couldn't plot a graph if you paid me. I faint at fractions and pain at parabolas. I'm happy I (barely) passed Maths with the minimum grade.

The point I'm making is, if it's extra credit, then aren't you supposed to figure it out for yourself instead of asking other people to do it for you?

Edit: I see where you got simple from...I reposted this post from another thread that was simple
Last edited by Kinks>Stones at Feb 26, 2008,
#37
Quote by chubbychunks
So can't you just integrate the directrix and make it = 0?



I'm sorry but I don't know what that means and have never done any integrating of directrices.
#39
Quote by Kinks>Stones
Simple?!

I couldn't plot a graph if you paid me. I faint at fractions and pain at parabolas. I'm happy I (barely) passed Maths with the minimum grade.

The point I'm making is, if it's extra credit, then aren't you supposed to figure it out for yourself instead of asking other people to do it for you?



Well the fact of the matter is that I don't have a clue how to do it, nor can I find a way from my book. And although I am asking other people, I'm also looking for resources myself, but it really isn't a life or death situation in which I'm relying on others to get through a crucial part of my life, and it's not a recurring thing that I do.
#40
doesn't he need the formula for parabola before he can differentiate it?
tl;dr : IM BETTER THAN YOU
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