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Homework Help: Help me confirm

  1. Apr 30, 2005 #1
    hey , i tried deriving another method for solving a quadratic equation ,and here is wat i came across
    +or - sqrt ([b^2-2ac+or-(b sqrt[b^2-4ac])/2a^2) i hope u get this correctly
    its read plus or minus square root of b^2-2ac plus or minus b root b^2-4ac

    all divided by 2a^2,remember the first root is common to all functions.i know u will get four values of which 2 will be eligible.pls help me confirm the formula for all eqns.thnxs
  2. jcsd
  3. Apr 30, 2005 #2
  4. Apr 30, 2005 #3


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    I notice nobody has responded yet, maybe they know something I don't. But I'm going to give you the benefit of the doubt once and assume that you are posting the legitimate results of your efforts. If it turns out you're just posting nonsense to spam the forums, then I'm wasting my time. We'll see.

    I interpret what you wrote as this:

    [tex] \pm \sqrt{ b^2 - 2ac \pm \frac{b\sqrt{b^2-4ac}}{2a^2}} [/tex]

    I'm curious to see how you "derived" it. I have to say I'm very doubtful that this is a correct formula. For two reasons:

    1. It's only valid if it is equivalent to the standard quadratic formula, and I couldn't get it to the standard form using algebraic manipulations, not that I tried very hard. Also, if it is correct, ie equivalent to the existing quadratic formula, then it is useless, because it is in a much more complicated form than the standard quadratic formula.

    2. A formula for calculating the roots of a quadratic should return only two roots, no more, no less. If the coefficients a, b, and c are real numbers, then those roots should be either real and distinct, or a real double root, or a complex conjugate pair. It makes no sense that 2 legitimate roots and 2 dummy roots would be returned.

    In other words, you have some explaining to do... :tongue2:

    Edit: Have you seen the derivation of the real quadratic formula, and/or tried it yourself? I think it would be a useful exercise. Start with a quadratic polynomial in the form:

    [tex] ax^2 + bx + c [/tex]

    Complete the square, and solve for x.
    Last edited: Apr 30, 2005
  5. Apr 30, 2005 #4
    If your interpretation of the original ASCII version of the new "quadratic equation" is right, then it's wrong by a simple inspection. The simplest quadratic equation


    will have solutions of [tex]\sqrt{2}[/tex] and [tex]-\sqrt{2}[/tex] via his method while we all know the solution is -1 with multiplicity 2, just to change things up a bit :biggrin:
  6. May 1, 2005 #5
    not that cepheid,2a^2 is a denominator to all not just bsqrt....
  7. May 1, 2005 #6
    so pls give it another try houserichichi
  8. May 1, 2005 #7


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    Is it too difficult for you to read the responses you get? You have two [itex]\pm[/itex] in you formula. How many solutions to a quadratic equation does that give you? How many solutions does a quadratic equation have?

    What solutions does your formula give for x2- 2x+ 1= 0?

    You are going to have to do something with those [itex]\pm[/itex]s!

    Would you mind showing us how you derived that formula.

    By the way: 1) It's not a good idea to give your e-mail address out publicly.
    2) If you have to call yourself "boygenius" then you aren't!
  9. May 3, 2005 #8
    thnxs hallsofivy ,but for the mail, it was opened at first for me by my brother and i have been using it so u see i can not change it for another or els i would have
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