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Homework Help: Description of binomial expansion

  1. Oct 17, 2011 #1
    what will be the coefficient of the x^n in the expansion of (1+x)^-1 and(1-x)^-1. Please answer it separately..
  2. jcsd
  3. Oct 17, 2011 #2
    According to the spirit of this forum, an attempt on your part will help to encourage someone to help you.
  4. Oct 17, 2011 #3
    i used the general term as tr=C(n,r) a^(n-r)*x^r. however i could not hav a final answer as i supposed this method is not approate so there may be other wayz to solve. and using above formula i always got the answer without the appropriate sign..could anyone help for it..
  5. Oct 17, 2011 #4
    You can use

    (1 + x)[itex]^{m}[/itex] = 1 + mx/(1!) + m(m - 1)x[itex]^{2}[/itex]/(2!) + ...
  6. Oct 17, 2011 #5
    ya i used it but what should be the nth term...i have no idea...pls give me some..
  7. Oct 18, 2011 #6

    Ray Vickson

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    I am sure you have seen the answers to these questions, even before you ever heard of the binomial expansion!

  8. Oct 18, 2011 #7


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    I believe Ray Vickson is referring to the formula for the infinite geometric sum.
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