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Math Help - question.

  1. #1
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    question.

    why cant you cancel the (-1)'s in this fraction? ...they just solved the problem.
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  2. #2
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    If you work it out:

    2(-1)-1(4)
    (-1)^2

    is equal to -6. However if we cancel the (-1) on top so it's just 2(1) and cancel (-1)^2 to become just (-1) we get:

    2(1)-1(4)

    (-1)

    which is 2. The problem is you have that " -1(4) " bit at the end. If it were just:

    2(-1)
    (-1)^2

    Then you could definitely cancel the (-1). However, the " -1(4) " part screws it up! Hope this helps.
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  3. #3
    Super Member Bacterius's Avatar
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    You can cancel it ! Look :

    \frac{2(-1) - 1(4)}{(-1)^2}

    \frac{-2 - 4}{(-1)^2}

    \frac{-(2 + 4)}{(-1)^2}

    \frac{(-1)(2 + 4)}{(-1)^2}

    \frac{2 + 4}{-1}

    \frac{-(2 + 4)}{1}

    -(2 + 4)

    -2 - 4

    -6

    Does it make sense ?
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  4. #4
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    Your math makes perfect sense. However, i believe mojojojo meant why can't you cancel the (-1)'s in the first step of the equation. Which you can not. Am i wrong?
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  5. #5
    Super Member Bacterius's Avatar
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    Yes, you are right. One has to rearrange it and factorize it first before cancelling out the minus 1.
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