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Thread: When are numbers negative?

  1. #1
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    When are numbers negative?

    I did two problems just now and both had positive answers, while I mistakenly got negative answers.

    The first, $\displaystyle 16x^2 - 16x^2 - 3x$
    I thought it would equal 3x, since x - x = 0 and 0 - 3x = -3x

    The other, $\displaystyle \frac{6x^2}{x^2-1}=6$ While I got the opposite answer.
    Can anyone explain why these answers aren't positive?
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  2. #2
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    Re: When are numbers negative?

    Just multiply -3x by minus one.

    For the second problem:

    $\displaystyle \frac {6x^2}{x^2 - 1} = 6 $

    $\displaystyle \frac {x^2 - 1}{6x^2} = \frac {1}{6} $

    $\displaystyle (6)(x^2 - 1) = (1)(6x^2) $

    $\displaystyle 6x^2 - 6 = 6x^2 $

    $\displaystyle (6x^2 -6x^2) -6 = 0$

    $\displaystyle 0 - 6 = 0 $

    $\displaystyle -6 = 0 $

    $\displaystyle (-6)(-1) = (0)(-1) $

    $\displaystyle 6 $

    You could have just multiplied out $\displaystyle x^2 - 1 $ instead.
    Last edited by astartleddeer; Jul 20th 2012 at 06:00 AM.
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  3. #3
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    Re: When are numbers negative?

    Quote Originally Posted by Nervous View Post
    I did two problems just now and both had positive answers, while I mistakenly got negative answers.

    The first, $\displaystyle 16x^2 - 16x^2 - 3x$
    I thought it would equal 3x, since x - x = 0 and 0 - 3x = -3x

    The other, $\displaystyle \frac{6x^2}{x^2-1}=6$ While I got the opposite answer.
    Can anyone explain why these answers aren't positive?
    what does "the first" mean ? I don't see an equation ...

    fyi, the second equation has no solution for x.
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