Results 1 to 3 of 3

Math Help - Find the equation for the parabola...

  1. #1
    Newbie
    Joined
    Mar 2010
    Posts
    6

    Find the equation for the parabola...

    Find the equation for the parabola that has its focus on the positive x-axis, 4 units away from the directrix.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,719
    Thanks
    635
    Hello, uselessjack!

    Is there more information?
    There are four forms of the parabola, each with its own equation.

    I'll derive one of them . . .


    Find the equation for the parabola that has its focus on the positive x-axis,
    4 units away from the directrix.
    This is a "vertical" parabola, opening upward.


    The focus is at F(f,0)
    The directrix is: y = -4
    Code:
                |
                |
            *   |                   *
                |       F
        - - -*- + - - - o - - - - -* - - 
              * |     (f,0)       *
                *       :       *
                |  *    :    * 
                |       o V
                |     (f,-2)
                |       :
                |       :
          - - - + - - - + - - - - -
              -4|
                |

    The equation has the form: . (x-h)^2 \:=\:4p(y-k)

    The vertex is at: . V(f,-2)

    The value of p is: . p \,=\,2


    The equation is: . (x-f)^2 \:=\:4(2)\left(y-[-2]\right) \quad\Rightarrow\quad (x-f)^2 \:=\:8(y+2)

    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2010
    Posts
    6
    Thank you for your help and time. I am left with confusion still. I thought there would be a specific answer. I am given five choices and still can't figure out which one is correct.

    4y^2 = 4x
    y^2 = 4x
    y^2 = 8x
    x^2 = 16y
    4y^2 = x
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: March 22nd 2011, 04:57 PM
  2. Find an equation of the parabola?
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: March 19th 2010, 12:27 PM
  3. Find equation of the parabola
    Posted in the Geometry Forum
    Replies: 1
    Last Post: February 17th 2010, 11:04 AM
  4. Find parabola equation
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: July 14th 2008, 02:55 AM
  5. Find Equation Of Parabola
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: April 8th 2007, 07:46 AM

Search Tags


/mathhelpforum @mathhelpforum