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binomial expansion questions..

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    is anyone willing to check these for me?
    1) What is the coefficient of y^3 in the expansion of (1+y^6)
    A: 20y^3
    2) The coefficient of a^2b^5 in the expansion of (a+b)^7
    A: 21a^2+b^5
    3) the term a^2b^3 in the expansion of (a+2b)^5
    A: 80a^2b^3
    4) The expansion of (x+y)^8 contains the term
    a- x^7y
    b- 56x^2y^6
    c-56x^3y^5
    d-84x^4y^4
    e-8y^8
    I said c
    Thanks very muchly xxxxx
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    Haven't done Binomial Expansion for a while, but I gave them a shot and got pretty much the same: Q1 is correct, Q2 is correct, (although I'm not sure why you've stuck a plus sign in your answer...), Q3 was the only one I differed on, but that's probably because I haven't done this stuff in a while - I don't know where 80 was from, but assume you're right..., and Q4 is correct.
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    yes.
    well, yes, but that plus sign shouldn't be there.
    yes.
    yes.
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    thanks, i think the plus sign was a typo.
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    Happy to be of help!

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Updated: February 16, 2009
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