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Thread: Quadratic Equations

  1. #1 Quadratic Equations 
    New Member NurBoEFZZJ's Avatar
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    Apr 2008
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    Ok I know the formula by heart and I know how to fill in everything
    but lets say the equation has all of the numbers filled in

    a=?
    b=?
    c=?

    I add and multiple everything together but what do I do after this?


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  3. #2  
    Forum Radioactive Isotope MagiMaster's Avatar
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    It's pretty simple. For a*x<sup>2</sup> + b*x + c = 0, you plug in a, b and c and get 2 numbers. We'll call them q<sub>1</sub> and q<sub>2</sub>. Then a*x<sup>2</sup> + b*x + c = 0 implies (x - q<sub>1</sub>)*(x - q<sub>2</sub>) = 0. This also means that q<sub>1</sub> and q<sub>2</sub> are zeroes of the equation (plug either back in for x and you'll get 0).


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  4. #3  
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    You solve the quadratic equation and this will give you the answer for x. Because the quadratic equation has a +/- sign in it you will get two answers, called roots. Often, one of the roots will make no sense, depending on the context of the problem. For example, if you are using the quadratic equation to solve for the length of a side of a rectangle, it could not have a side with a negative length. In that case, throw out the unreasonable answer, and use the one that makes sense.
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