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Math Help - [SOLVED] please help

  1. #1
    Moondancer
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    [SOLVED] please help

    How do you solve this ?


    (-a) 5 + (-a)3 = ???

    The book says the result is 8 but how do you get to that ??

    (3 and 5 a 'to the power'.shoud be above right bracket but dont know how to write it)
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  2. #2
    Bar0n janvdl's Avatar
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    Quote Originally Posted by Moondancer View Post
    How do you solve this ?


    (-a) 5 + (-a)3 = ???

    The book says the result is 8 but how do you get to that ??

    (3 and 5 a 'to the power'.shoud be above right bracket but dont know how to write it)
     (-a)^{5} + (-a)^{3} = 8 ?
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Moondancer View Post
    How do you solve this ?


    (-a) 5 + (-a)3 = ???

    The book says the result is 8 but how do you get to that ??

    (3 and 5 a 'to the power'.shoud be above right bracket but dont know how to write it)
    "8" is wrong, unless there's a typo.

    First, we have that (-a)^n = (-1)^na^n = -1 \cdot a^n when n is odd. So:
    (-a)^5 + (-a)^3 = -a^5 + -a^3

    The only thing I can think of to do from here is to factor it:
    = -a^2(a^2 + 1)

    By the way, to type powers without using LaTeX, use (-a)^5, etc.

    -Dan
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  4. #4
    Member disclaimer's Avatar
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    I agree with the others, there must be some mistake. I don't think we can get a "pure" number by solving (-a)^{5} + (-a)^{3}.
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