Results 1 to 2 of 2

Math Help - finding equation of a parabola

  1. #1
    Junior Member
    Joined
    Jul 2009
    Posts
    32

    finding equation of a parabola

    hiii i just need some help finding the equation of a parabola that has the points (-a,0), (a,0) and (0,a/2)

    this is based on a volume of revolution question,
    a hemispherical bowl of radius a units is filled with water to a depth of a/2 units. find by integration the volume of the water

    i just really need some help with this because i tried simultaenous equations for the equation of the parabola and i got
    (-1/4)a(x^2)+(1/4)x+(a/2)
    can anyone tell me if this equation is right for the parabola because i dont think it is
    thankyou to anyone who can help me !! =)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Nov 2008
    Posts
    461
    Hi.

    Quote Originally Posted by flyinhigh123 View Post
    hiii i just need some help finding the equation of a parabola that has the points (-a,0), (a,0) and (0,a/2)

    this is based on a volume of revolution question,
    a hemispherical bowl of radius a units is filled with water to a depth of a/2 units. find by integration the volume of the water

    i just really need some help with this because i tried simultaenous equations for the equation of the parabola and i got
    (-1/4)a(x^2)+(1/4)x+(a/2)
    can anyone tell me if this equation is right for the parabola because i dont think it is
    thankyou to anyone who can help me !! =)
    Your solution is not correct.

    Let f(x):=(-1/4)a(x^2)+(1/4)x+(a/2)

    f(a) = -a^3/4+a/4+a/2 != 0

    You already know that -a and +a is a zero of f, so

    f(x) = (x+a)(x-a)

    but f(0) should be a/2

    so

    f(0) = a*(-a) = -a^2

    Thus something is missing

    -a^2*missing = a/2

    missing = -1/(2a)

    Hence

    f(x) = (x-a)(x+a)*[-1/(2a)]

    Done

    Yours
    Rapha
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Finding the equation of parabola
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 16th 2011, 12:20 PM
  2. Finding the equation of a parabola
    Posted in the Geometry Forum
    Replies: 1
    Last Post: January 16th 2011, 06:29 PM
  3. Finding the equation of a parabola
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 3rd 2010, 12:19 AM
  4. Finding Equation for parabola
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: December 5th 2009, 11:27 PM
  5. Help with finding the equation of a parabola
    Posted in the Algebra Forum
    Replies: 2
    Last Post: June 1st 2009, 06:33 PM

Search Tags


/mathhelpforum @mathhelpforum