My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Reply
 
LinkBack Thread Tools Display Modes
May 18th, 2015, 06:53 AM   #1
Member
 
Joined: Sep 2014
From: Sweden

Posts: 94
Thanks: 0

Question Find "Focus and Control Line of Parable"

So I have this equation in my math book.

$\displaystyle
(x^2)/2
$

This is the "orginal" formula for a parable.

Focus: (0, a)
Control line: y = -a
$\displaystyle
(x^2)/4a
$

They want me to find the focus and the control line of the parable. I have found two coordinates that the parable will hit and that is:

( 2, 2 ) and ( 4, 8 )

But I have no idea of how to find the focus and control line . . .

Thanks for help!
DecoratorFawn82 is offline  
 
May 18th, 2015, 07:36 AM   #2
Banned Camp
 
Joined: Jun 2014
From: Earth

Posts: 945
Thanks: 191

Quote:
Originally Posted by DecoratorFawn82 View Post
So I have this equation in my math book.


(x^2)/2 $\displaystyle \ \ \ $y = (x^2)/2 <----- This is an equation.


This is the "orginal" formula for a parable. $\displaystyle \ \ \ $It's spelled "parabola."

Focus: (0, a)
Control line: y = -a $\displaystyle \ \ \ \ $What you call a "control line" is typically called a "directrix."


(x^2)/4a $\displaystyle \ \ \ \ $ This should be an equation and written, for example, as y = (x^2)/(4a).


They want me to find the focus and the control line of the parable.

I have found two coordinates that the parable [parabola] will hit and that is:
( 2, 2 ) and ( 4, 8 ) $\displaystyle \ \ \ \ $Those points are on there, but you don't need them for this problem.

But I have no idea of how to find the focus and control line . . .

Thanks for help!
The vertex is always halfway between the focus and the directrix.


y = (x^2)/2 = (x^2)/(4a)

So set 2 = 4a and solve for a:

2 = 4a

1/2 = a


You stated your focus is (0, a) and your control line (directrix) is y = -a.

Now make the substitutions with the a-value.


- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


Here are some Internet sites that discuss the vertex, focus, and directrix
(what you called a "control line") for a parabola:

https://www.google.com/#q=parabola+focus+directrix


.

Last edited by Math Message Board tutor; May 18th, 2015 at 07:40 AM.
Math Message Board tutor is offline  
May 18th, 2015, 07:58 AM   #3
Math Team
 
Joined: Oct 2011
From: Ottawa Ontario, Canada

Posts: 14,597
Thanks: 1039

y = (x^2)/(4a)

y = x^2 / (4a) is sufficient.
Denis is offline  
May 18th, 2015, 08:13 AM   #4
Member
 
Joined: Sep 2014
From: Sweden

Posts: 94
Thanks: 0

I'm sorry about that I use wrong words for some mathematical things. But it's a huge difference between what we call these things in Swedish and in English.

But thanks for help, that was the answer I was looking for

EDIT:

How would I find the focus if I weren't given it (Focus: (0, a)) or is this the formula
that is right for all parabolas? Or how would I otherwise do?

Last edited by DecoratorFawn82; May 18th, 2015 at 08:36 AM.
DecoratorFawn82 is offline  
May 18th, 2015, 10:03 AM   #5
Math Team
 
Joined: Oct 2011
From: Ottawa Ontario, Canada

Posts: 14,597
Thanks: 1039

Quote:
Originally Posted by Math Message Board tutor View Post
y = (x^2)/2
I am officially "scolding" you for your ignorance.
You are confusing students with redundant brackets.
If your explanation for the above goof is to add clarity,
then this is required: y = (x^2)/(2).

I'll be reporting this post of yours
to the STD (Suspected Trolls Department).

You're in trouble deep: the STD CEO
is none other than Sir Jonah The Guzzler
Denis is offline  
May 19th, 2015, 04:09 AM   #6
Member
 
Joined: Sep 2014
From: Sweden

Posts: 94
Thanks: 0

What?! I try to explain as well as I can. And I try to write the words correct words in mathematics in English.

I'm writing as well as I can and I try to explain what I mean. I don't really get why you would report my posts? I'm only asking for help because I don't know how to solve these problems on my own.

And no I'm not trying to troll someone. My posts are serious and I will try to do better in my explanations then. I'll do as good as I can.
DecoratorFawn82 is offline  
May 19th, 2015, 05:15 AM   #7
Math Team
 
Joined: Oct 2011
From: Ottawa Ontario, Canada

Posts: 14,597
Thanks: 1039

That was NOT addressed to you...and is only a joke...OK?

You're doing quite good for someone learning English.
Denis is offline  
May 19th, 2015, 05:29 AM   #8
Member
 
Joined: Sep 2014
From: Sweden

Posts: 94
Thanks: 0

I didn't see that at first. Okay. Thank you then!
DecoratorFawn82 is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
find



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Straight line "fun" Denis Geometry 10 June 11th, 2014 11:56 AM
A "simple" application of dirac delta "shift theorem"...help SedaKhold Calculus 0 February 13th, 2012 11:45 AM
"separate and integrate" or "Orangutang method" The Chaz Calculus 1 August 5th, 2011 09:03 PM
sample exeriment-need help finding "statistic" and "result" katie0127 Advanced Statistics 0 December 3rd, 2008 01:54 PM
terms "non-increasing" or "non-decreasing" Ujjwal Number Theory 2 September 29th, 2008 07:06 AM





Copyright © 2019 My Math Forum. All rights reserved.