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Math Help - simplifying an expression with exponents, such that x=-1

  1. #1
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    simplifying an expression with exponents, such that x=-1

    If I want to simplify the following expression such that x= -1:

    -9x2 - x + 1
    ___________
    x3 + x

    How do I input the value of -1 into -9x2?

    like this -9(-1)2 which simplifies to -9(1) which equals -9

    or like this -9(-12) which simplifies to -9(-1) which equals positive 9

    I ask this because I know that exponents only apply to the value or parenthetical expression right next to it. In the former case, (-1) times (-1) is positive 1. In the latter case, the square only applies to the 1 and not to the minus sign which is then left over after the 1 is squared. So, this yields a -1.

    So, which way is right??
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  2. #2
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    Re: simplifying an expression with exponents, such that x=-1

    x^{2} is shorthand notation for x multiplied by x.
    Substitute x=-1 and you get x^{2}=x.x=(-1).(-1)=1
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  3. #3
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    Re: simplifying an expression with exponents, such that x=-1

    remember your order of operations?

    -9(-1)^2

    evaluate exponents first ...

    -9(1)

    then multiply ..

    -9
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  4. #4
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    Re: simplifying an expression with exponents, such that x=-1

    Quote Originally Posted by skeeter View Post
    remember your order of operations?

    -9(-1)^2

    evaluate exponents first ...

    -9(1)

    then multiply ..

    -9
    Actually, the first letter in PEMDAS (which I first learned as "Please Excuse My Dear Aunt Sally") is "P" which stands for "parentheses". That is why it is specifically (-1)^2= 1, not -(1^2)= -1.
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