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Combinations Problem

  1. May 20, 2008 #1
    1. The problem statement, all variables and given/known data
    http://img234.imageshack.us/img234/8519/combgf7.png [Broken]​

    2. Relevant equations

    3. The attempt at a solution
    The picture I have shown contains the problem and the teacher's solution. However, I was wondering how the [tex]k[/tex] value is 3. And no, I can't ask the teacher; my test is tomorrow.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. May 20, 2008 #2


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    This is how I would do it



    and you want the coefficient of [itex]x^11[/itex]

    so if you expand you will get


    You need to find k and you want the power of x to be 11

    so that 3k-10=11

    See it?
  4. May 20, 2008 #3
    For your expansion, isn't the 1 supposed to be where the [tex]x^3[/tex] is? Because 1 is the y value, while [tex]x^3[/tex] is the x value.

    Also, k doesn't equal 3 in [tex]3k-10=11[/tex]
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