Results 1 to 5 of 5

Math Help - Find an equation of the parabola?

  1. #1
    Member
    Joined
    Nov 2009
    Posts
    87

    Find an equation of the parabola?

    Question says to find an equation of the parabola:
    Vertex (-1, 2); Focus (-1, 0)

    How do I do this? I am confused.

    Thanks for any help.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    Quote Originally Posted by iluvmathbutitshard View Post
    Question says to find an equation of the parabola:
    Vertex (-1, 2); Focus (-1, 0)

    How do I do this? I am confused.

    Thanks for any help.
    You can find the equation by this formula:

     y = a{(x-h)^2}+k

    where, (h,k) is your vertex

    and a= \frac{1}{4d} ; d is the distance from the vertex to the focus.

    So use distance formula (with the coordinates of your vertex and focus) to find d. You already have (h,k) as your vertex. Plug these values in to get the equation of your parabola.

    Try doing it and post a message if you come up with errors
    Last edited by harish21; March 19th 2010 at 12:22 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Nov 2009
    Posts
    87
    so..
    y = 1/8 (x - 1)^2 + 2

    Is this right?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor harish21's Avatar
    Joined
    Feb 2010
    From
    Dirty South
    Posts
    1,036
    Thanks
    10
    Quote Originally Posted by iluvmathbutitshard View Post
    so..
    y = 1/8 (x - 1)^2 + 2

    Is this right?
    Note:

     y = a{(x-h)^2}+k

    you have h = -1

    so your equation will be:

     y = \frac{1}{8}{(x+1)^2}+2
    Follow Math Help Forum on Facebook and Google+

  5. #5
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    11
    Awards
    1
    Quote Originally Posted by iluvmathbutitshard View Post
    so..
    y = 1/8 (x - 1)^2 + 2

    Is this right?
    Hi iluvmathbutitshard,

    Almost, you missed the sign on "a".


    Another way to find "a" in y=a(x-h)^2+k

    is by knowing that the focus has coordinates \left(h, k+\frac{1}{4a}\right)

    Set the second coordinate of this ordered pair to the second coordinate of your focus and we have

    2+\frac{1}{4a}=0

    Solving this, you get a=-\frac{1}{8}

    Your parabola opens down.

    y=-\frac{1}{8}(x+1)^2+2
    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 the equation for the parabola...
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: April 8th 2010, 07:01 PM
  3. Parabola - find the equation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 22nd 2010, 10:44 PM
  4. Find equation of the parabola
    Posted in the Geometry Forum
    Replies: 1
    Last Post: February 17th 2010, 11:42 AM
  5. How to find the equation of a Parabola
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: June 1st 2009, 08:27 PM

Search Tags


/mathhelpforum @mathhelpforum