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    Hi Ive got this question to do for homework and I cant seem to do it !

    Find: the value of the term in the expansion of (x-1/x)^8 which is independent of x

    the answer is 70 by the way

    Thanks
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    Are you sure it is 70?
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    Here's one way to do it which makes it a bit easier:

    (x-\frac{1}{x}) = \frac{x^2-1}{x}

    Then (x-\frac{1}{x})^8 = (\frac{x^2-1}{x})^8 = \frac{(x^2-1)^8}{x^8}

    Then notice that the terms independent of x will be the coefficient of the x^8 term in the expansion of (x^2-1)^8.
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    (Original post by DeanK2)
    Are you sure it is 70?
    Yes, it is.
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    (Original post by Simba)
    Yes, it is.
    yeah - just did the choose thing on the calculator,I suck at mental maths
 
 
 
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Updated: November 11, 2008
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