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Math Help - Quadratic Equation

  1. #1
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    Quadratic Equation

    Hi,

    I don't think I'm getting the correct roots for this equation...

    3x2(squared)- 2x- 6 = 0

    That should read 3xsquared.

    I had to use the b +/- formula and I'm getting x= 1.79 or x= -1.12

    That can't be right???
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  2. #2
    Senior Member euclid2's Avatar
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    Quote Originally Posted by Larianne View Post
    Hi,

    I don't think I'm getting the correct roots for this equation...

    3x2(squared)- 2x- 6 = 0

    That should read 3xsquared.

    I had to use the b +/- formula and I'm getting x= 1.79 or x= -1.12

    That can't be right???
     3x^2 - 2x - 6 = 0

    Use the quadratic equation  -b+/- square root of \frac{b^2 -4ac}{2a}

    Where a is 3, b is -2 and c is -6.
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  3. #3
    o_O
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    Let's format that a little better: x = \frac{b \pm \sqrt{b^2 - 4ac}}{2a}

    Why don't you think that's right? You rounded off to a few decimal places which will throw off your answer a little bit but it is correct (again, rounded of course)
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  4. #4
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    Quote Originally Posted by euclid2 View Post
     3x^2 - 2x - 6 = 0

    Use the quadratic equation  -b+/- square root of \frac{b^2 -4ac}{2a}

    Where a is 3, b is -2 and c is -6.
    Yes, I've done that but I put my answers back into the equation to check and I'm not getting zero.
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  5. #5
    Senior Member euclid2's Avatar
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    Quote Originally Posted by Larianne View Post
    Yes, I've done that but I put my answers back into the equation to check and I'm not getting zero.
    x = \frac{2 \pm \sqrt{-2^2 - 4(3)(-6)}}{2(3)}
    x = \frac{2 \pm \sqrt{76}}{6}
    x = \frac{2 + \sqrt{76}}{6} +
    x = \frac{2 - \sqrt{76}}{6}
    Therefore,  x =1.78  +  x=-1.12
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  6. #6
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    Quote Originally Posted by o_O View Post
    Let's format that a little better: x = \frac{b \pm \sqrt{b^2 - 4ac}}{2a}

    Why don't you think that's right? You rounded off to a few decimal places which will throw off your answer a little bit but it is correct (again, rounded of course)
    Should it not work out evenly???
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  7. #7
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    Quote Originally Posted by euclid2 View Post
    x = \frac{2 \pm \sqrt{-2^2 - 4(3)(-6)}}{2(3)}
    x = \frac{2 \pm \sqrt{76}}{6}
    x = \frac{2 + \sqrt{76}}{6} +
    x = \frac{2 - \sqrt{76}}{6}
    Therefore,  x =1.78  and  x=-1.11
    So my answer is okay or should it be your answer???
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  8. #8
    Senior Member euclid2's Avatar
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    Quote Originally Posted by Larianne View Post
    So my answer is okay or should it be your answer???
    Your answer is fine. Good job.
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