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Math Help - using the quadratic formula

  1. #1
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    using the quadratic formula

    I need help factoring this trinomial:

    12x^2 -88x+112 =0


    I tried using the quadratic formula and getting:
    x=90.02758... or 85.9724.... which both don't make any sense whatsoever. I think I am making mistakes simplifying the quadratic formula. I get to [88 +/- sqrt(2368)]/24

    What next?


    my course is saying the factors are:

    x=5.694 or 1.639
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  2. #2
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    Re: using the quadratic formula

    Quote Originally Posted by jmanna98 View Post
    I need help factoring this trinomial:
    12x^2 -88x+112 =0
    First simply the question: 3x^2-22x+28=0.
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  3. #3
    Member anonimnystefy's Avatar
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    Re: using the quadratic formula

    hi jmanna98

    you can first divide the first equation by 4,getting:
    3x^2-22x+28=0

    then use the quadratic formula:
    x_{1/2}=\frac{-(-22)\pm \sqrt{22^2-4\cdot 3\cdot 28}}{2\cdot 3}

    can you simplify this now?
    Last edited by anonimnystefy; August 18th 2011 at 02:11 PM.
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  4. #4
    Super Member bigwave's Avatar
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    Re: using the quadratic formula

    where does the -88 come from thot b=(-22)


    x=\frac{-b\mp\sqrt{b^2-4ac}}{2a}
    Last edited by bigwave; August 18th 2011 at 02:19 PM.
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  5. #5
    Member anonimnystefy's Avatar
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    Re: using the quadratic formula

    oh yes you are right.i will correct that now.thanks!
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  6. #6
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    Re: using the quadratic formula

    Yes that made things easier. Thanks for that
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  7. #7
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    Re: using the quadratic formula

    Quote Originally Posted by jmanna98 View Post
    Yes that made things easier.
    OK: 3000x^2 -3000x - 6000 = 0 ; x = ?
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  8. #8
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    Re: using the quadratic formula

    Quote Originally Posted by jmanna98 View Post
    I need help factoring this trinomial:

    12x^2 -88x+112 =0


    I tried using the quadratic formula and getting:
    x=90.02758... or 85.9724.... which both don't make any sense whatsoever. I think I am making mistakes simplifying the quadratic formula. I get to [88 +/- sqrt(2368)]/24
    According to my calculator, \sqrt{2368}= 48.66, to two decimal places. Adding 88 gives 136.66 and dividing that by 24, 5.69 as your course gives.

    Oh, I see what your error is. You have [88+/- sqrt(2369)]/24, which is correct, but you did 88+/- sqrt(2368)/24! Do you see the difference? The [ ] means you do the sum and difference before dividing by 24. If you entered, on your calculator, "88+ sqrt(2368)/24" you will be dividing only the square root by 24, not the sum. Either use parenthesis keys or, simpler, press the "=" key before the square root.

    What next?


    my course is saying the factors are:

    x=5.694 or 1.639
    I hope it didn't! The roots of the equation are 5.694 and 1.639 (to three decimal places) but the factors of the trinomial are 12(x- 5.694)(x- 1.639).
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  9. #9
    Member anonimnystefy's Avatar
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    Re: using the quadratic formula

    Quote Originally Posted by Wilmer View Post
    OK: 3000x^2 -3000x - 6000 = 0 ; x = ?
    first you should divide everything by 3000 to get:
    Spoiler:
    x^2-x-2=0
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  10. #10
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    Re: using the quadratic formula

    Hmmm...I was asking jmanna98, the original poster...to see if he could now handle these...
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