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Homework Help: Discriminants for ellipse, parabola or hyperbola

  1. Dec 3, 2008 #1
    1. The problem statement, all variables and given/known data

    Use the discriminant to determine if the following are equations of an ellipse, parabola or hyperbola

    [tex]6x^2-12xy+6y^2-5x+9=0[/tex]
    [tex]5xy-4y^2+8x-3y+20=0[/tex]
    [tex]x^2-9xy+5y^2-2=0[/tex]
    [tex]10x^2-9xy+5y^2-2=0[/tex]
    [tex]2y^2-10x+9y-8=0[/tex]

    2. Relevant equations

    3. The attempt at a solution

    I got these answers:

    [tex]0, parabola[/tex]
    [tex]25, hyperbola[/tex]
    [tex]44, hyperbola[/tex]
    [tex]-119, ellipse[/tex]
    [tex]0, parabola[/tex]

    could someone check me on these? Thanks!
     
  2. jcsd
  3. Dec 3, 2008 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Re: Discriminants

    Shouldn't the third one be 81-4*1*5=61,hyperbola? Was that so hard you really needed a check?
     
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