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Homework Help: Easy question, simple algebra

  1. Jun 11, 2009 #1
    1. The problem statement, all variables and given/known data

    This is just a question about order of operations. I recently started working through Morris Kline's "Calculus: An Intuitive and Physical Approach", but unfortunately my algebra's a bit rusty and the book doesn't list answers. I searched around via Google but I couldn't find any answers to this particular question.

    2. Relevant equations

    f(x) = -x^2

    3. The attempt at a solution

    I'm not sure how to deal with the negative sign here or in similar equations. If I'm solving for x = some number, let's say 2 [i.e. f(2)], do I apply the exponent and then apply the negative sign (so the answer would be -4)? I remember something from school about how you can treat the minus sign as a -1 multiplied by whichever relevant quantities in some situations. In this case, I might rewrite the equation as f(2) = -1(2^2). Or, should I just treat the base as negative in this sort of situation, so the answer would be 4 (-2*-2)?

    In the same way, if I'm entering f(-2), would it be -4 [-1(-2*-2)], or would it be 4 (negatives cancel each other out)?

    Thanks, sorry if this question seems a bit trivial.
  2. jcsd
  3. Jun 11, 2009 #2


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    Homework Helper

    f(x)= -1*(x^2)

    do what is in the brackets first, in this case for x=2, get 22 then multiply by -1.
  4. Jun 11, 2009 #3


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    Staff: Mentor

    I wasn't sure about this one (whether a unary prefix operator is lower in precedence than multiplication), but you appear to be correct. At least wikipedia.org says so too:


  5. Jun 11, 2009 #4
    So you are you saying that is is correct to rewrite f(x) = -x^2 as f(x) = -1*(x^2)? I just want to make sure you didn't misunderstand my post. I remember the basic order of operations, at least as far as the acronym goes - PEMDAS. I know how to solve f(x) = -1*(x^2).
  6. Jun 11, 2009 #5
    yes, -x^2 = -1*(x^2)
  7. Jun 11, 2009 #6
    Okay, thanks all.
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