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Homework Help: Re: Expansion

  1. Mar 20, 2006 #1
    I have the equation 1/2(x-3)^2-18

    Now normally I have no trouble with expansion of brackets but for some reason this is puzling to me.


    I get 1/2x^2-3x-27

    I checked the answer with a maths package and it comes up with : -

    1/2x^2-3x-27/2 Why? What am I missing here. where does the 27/2 come in?

    I also get 1/2(x-3)(x-9) if I factorise it again? My pacckage obviously likes, multiple different factorisations.

    Anyway I'm a bit stumped, normally I don't have a problem with this sort of straightforward stuff but I'm stumped on this one?
  2. jcsd
  3. Mar 20, 2006 #2


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    Science Advisor

    To clarify, your expression is

    What do you get when you expand (x-3)^2? You're then going to want to take half of that ENTIRE expression (which means half of every term in it) and subtract 18 from your result.
    Last edited: Mar 20, 2006
  4. Mar 20, 2006 #3
    It is official I am an idiot:rolleyes: of course -13.5 =-27/2 (+4.5-18) thanks :smile:
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