Binomial expansion of a function with x raised to a power

  • Thread starter Dixanadu
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  • #1
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Main Question or Discussion Point

Hey guys.

So I need to know how to Binomial expand the following function
[itex]\frac{1}{(1-x^{2})}[/itex].

I need this because I have to work out [itex]\prod^{∞}_{i=1}[/itex][itex]\frac{1}{(1-x^{i})}[/itex] for i up to 6. But I have to do it with Binomial expansion. If i can learn how to do [itex]\frac{1}{(1-x^{2})}[/itex] then the rest of the powers should be the same.

I was under the impression that [itex]\frac{1}{(1-x^{2})}[/itex] can be binomial expanded as

[itex]1+(-1)(-x^{2})+(-1)(-2)\frac{(-x^{2})^{2}}{2!}+(-1)(-2)(-3)\frac{(-x^{2})^{3}}{3!}+...[/itex]

Is that correct?

Thanks guys!
 

Answers and Replies

  • #3
Office_Shredder
Staff Emeritus
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This is correct, and you probably want to observe that
(-1)/1! = -1
(-1)(-2)/2! = 1
(-1)(-2)(-3)/3! = -1

and you can probably guess the pattern as you continue.
 
  • #4
HallsofIvy
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Wait, wait- don't tell me. I'm still working on it!
 

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