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Homework Help: Quadratic Simultaneous Equation

  1. Sep 17, 2013 #1
    1. The problem statement, all variables and given/known data
    Solve the equation for x

    [itex]y^2 = 4x[/itex]

    [itex]x^2 = 4y[/itex]

    2. Relevant equations


    3. The attempt at a solution

    [itex]y^2 -4x = x^2 - 4y = 0[/itex]

    I have spent ages re-arranging and substituting in values but I just cannot solve this thing.
  2. jcsd
  3. Sep 17, 2013 #2


    User Avatar
    Gold Member

    Why don't you try to rearrange the second equation for y and sub into the first equation. This will give you an equation entirely in terms of x.
  4. Sep 24, 2013 #3
    [itex]y = 2\sqrt{x}[/itex]
    [itex]y = \frac{x^{2}}{4}[/itex]

    I still have no idea how to find [itex]x[/itex]
  5. Sep 24, 2013 #4


    Staff: Mentor

    You didn't do what CAF123 suggested, which was to solve for y in the second equation, and then substitute for y in the first equation.

    You solved for y in the second equation, but then solved for y (incorrectly) in the first equation. Note that if y2 = 4x, then y = 2√x is only one of two solutions.
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