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Basic algebra question

  1. Feb 4, 2013 #1
    Simplify [itex]-d^2+[9d+(2-4d^2)][/itex]

    [itex]-d^2+[9d+(2-4d^2)][/itex]

    [itex]d^2[-9d-2+4d^2][/itex]

    [itex]d^2+4d^2-9d-2[/itex]

    [itex]5d^2-9d-2[/itex]

    but wolfram says the answer is

    [itex]-5d^2-9d+2[/itex]

    What did I do wrong?
     
    Last edited by a moderator: Feb 4, 2013
  2. jcsd
  3. Feb 4, 2013 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Here is your error- first, you have dropped the "+" in front of the "[" but that may be just a typo- more importantly you have distributed the "-" in front of [itex]d^2[/itex] into the [itex][9d+(2- 4d^2)[/itex]. Where you were supposed to have -A+ B, you have A- B.

     
  4. Feb 4, 2013 #3
    −d2+[9d+(2−4d2)]

    −d2+9d+2−4d2

    -5d2 + 9d − 2
     
  5. Feb 5, 2013 #4

    Mark44

    Staff: Mentor

    Without any indication that the 2 in d2 is an exponent, what you have here is close to meaningless.
    At a minimum, use ^ to indicate exponents, and = for expressions that are equal, like this:

    -d^2 + [9d + (2 − 4d^2)]
    = -d^2 + 9d + 2 - 4d^2
    = -5d^2 + 9d + 2

    Even better is to write exponents that actually look like exponents, using the exponent feature that is available when you click Go advanced.

    -5d2 + 9d + 2
     
  6. Feb 5, 2013 #5

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    [itex]-d^2- 4d^2= -5d^2[/itex]
    You seem to be under the impresion that adding two negatives gives a positive. That is not true. That rule only holds for multiplication and division.

     
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