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Math Help - quadratic equations with fractions

  1. #1
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    Smile quadratic equations with fractions

    I can't understand how I can find the X's here...
    (x-4)(30/x+2)=30

    Thanks
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  2. #2
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    Quote Originally Posted by dgolverk
    I can't understand how I can find the X's here...
    (x-4)(30/x+2)=30

    Thanks
    Expand the brackets:

    <br />
(x-4)(30/x+2)=30+2x-\frac{120}{x}-8=30<br />
.

    Simplify a bit:

    <br />
2x-\frac{120}{x}-8=0<br />
.

    Multiply through by x:

    <br />
2x^2-8x-120=0<br />
.

    Now use the quadratic formula to solve for x

    RonL
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  3. #3
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    well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
    the book's answer is wrong? or I did something not right?
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  4. #4
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    Quote Originally Posted by dgolverk
    well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
    the book's answer is wrong? or I did something not right?
    Hello,

    the bad news first: The answers in your book are right. Maybe you can demonstrate what you've done. Then it's much easier to help you.

    Greetings

    EB
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  5. #5
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    Quote Originally Posted by dgolverk
    well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
    the book's answer is wrong? or I did something not right?
    Hello,

    that's what you should have done: Use the quadratic formula:

    x=\frac{-(-8) \pm \sqrt{64-4 \cdot 2 \cdot(-120)}}{2\cdot 2}

    x=\frac{-(-8) \pm \sqrt{64+960}}{2\cdot 2}

    x=\frac{-(-8) \pm 32}{2\cdot 2}

    x=\frac{40}{4}\ \vee \ x=\frac{-24}{4}

    Greetings

    EB
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  6. #6
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    intersting...

    I did exactly what you have done and got other answers..I guess I forgot something
    Thanks a lot!
    Last edited by dgolverk; April 12th 2006 at 09:01 AM.
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