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Math Help - Pure Math 1 Help & Expanding trinomial

  1. #1
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    Pure Math 1 Help & Expanding trinomial

    Hi,
    I have a couple of homework questions, can anyone help me please?

    1) Given that the expansion of (1+ax)^n begins 1+36x+576x^2, find the values of a and n.
    2) Determine the coefficient of p^4q^7 in the expansion of (2p-q)(p+q)^10.

    3. How to expand the entire trinomial: (10+9x3+8/(3x5) )3

    Thank you very much
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  2. #2
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    Re: Pure Math 1 Help & Expanding trinomial

    Hey ThanhPhungLe1112.

    Hint for 1: What is the formula for the first three terms of a binomial expansion? Can you get results for a in terms of two of the coefficients?
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  3. #3
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    Re: Pure Math 1 Help & Expanding trinomial

    um...This is what I have for number 1. I'm not sure if it's right

    nC0 (1)n(ax)0 + nC1 (1)n-1(ax)1 + nC2 (1)n-2(ax)2

    (1)(1)(1) + nC1 (1) (ax) + nC2 (1) (a2x2)


    nC1 (ax) = 36x
    nC1 (a) = 36


    nC2 (a2x2) = 576x2
    nC2 (a2) = 576


    But then from here on, I'm stuck.
    Please help!
    Thanks,
    Phung

    PS: I know that somehow you have to use the factorials formula, but I don't know how to apply it in this case.
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  4. #4
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    Re: Pure Math 1 Help & Expanding trinomial

    What is the relationship between nC1 and nC2? Once you have this you will get a simple relationship between n and a that doesn't involve factorials and you can solve for n and a.
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  5. #5
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    Re: Pure Math 1 Help & Expanding trinomial

    is it nC2 = nC1-n ? I'm really confused
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  6. #6
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    Re: Pure Math 1 Help & Expanding trinomial

    Expand out both and simplify and try and get one in terms of a ratio and a difference.
    Thanks from ThanhPhungLe1112
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  7. #7
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    Re: Pure Math 1 Help & Expanding trinomial

    okay, Thanks I got the answer for that problem.
    But I have another assigment. So I was supposed to make a powerpoint explaining how to expand trinomials. I made my powerpoint, but when we did peer review in class this morning, some people said that I made a mistake. I can't figure out what I did wrong though so can you please help me by viewing this powerpoint and point out the mistake? I don't think it's calculation error, because I don't think they had times to check calculations so I must have solved it wrong.

    This is do tomorrow so can you please help me????


    * I know I made a mistake. The answer was supposed to be 1000 + 2700x^3.........
    but beside that, is there anything else that I need to fix?
    Attached Thumbnails Attached Thumbnails Pure Math 1 Help & Expanding trinomial-1.jpg   Pure Math 1 Help & Expanding trinomial-2.jpg   Pure Math 1 Help & Expanding trinomial-3.jpg  
    Last edited by ThanhPhungLe1112; January 14th 2013 at 07:55 PM.
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