Results 1 to 2 of 2

Thread: Parabola question

  1. #1
    Junior Member
    Joined
    Jan 2010
    Posts
    25

    Parabola question

    Given
    $\displaystyle x^2-4x=y+4$
    Find the vertex, focus and directrix

    So i know that i need to complete the square
    $\displaystyle x^2-4x+4=y+4+4$

    $\displaystyle (x-2)^2=(y+8)$

    Vertex is at $\displaystyle (2,-8)$

    and im having a bit of trouble on the focus and directrix....

    Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    Jan 2010
    Posts
    25
    okay i figured it out...

    $\displaystyle (x-2)^2=a(y+8)$
    Since $\displaystyle (y+8)$ doesn't factor, then
    $\displaystyle a=1$
    general form is $\displaystyle x^2=4ay$
    set $\displaystyle 4a=1 => a=1/4$

    directrix @ $\displaystyle y=-8.25$
    focus @ $\displaystyle (2,-7.75)$

    gotta love when posting on here rings a bell.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Parabola Question
    Posted in the Algebra Forum
    Replies: 2
    Last Post: Nov 16th 2010, 04:40 AM
  2. Parabola question
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: Jun 6th 2010, 12:45 PM
  3. parabola question
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 26th 2009, 08:44 PM
  4. Parabola Question
    Posted in the Geometry Forum
    Replies: 3
    Last Post: May 5th 2009, 09:23 AM
  5. parabola question
    Posted in the Algebra Forum
    Replies: 1
    Last Post: Mar 28th 2009, 06:42 PM

Search Tags


/mathhelpforum @mathhelpforum