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    I dont understand what you do when you find when the expansion of a function is valid. I have gathered from examples that if it is:
    (1-2x)^-1
    valid for when 2x<1 so when x<1/2
    but dont quite get it, just seeing the pattern from examples. The question I have is stating whether the series expansion i got (2-2x+10x^2) is valid for x=1/2. I thought you got when it is valid from the orginal function you expand?!?!
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    It's all about whether the series you get converges.

    Sometimes you can expand the same expression in different ways, and you might choose the one that does the job.

    I don't get what specific series you are working on.

    (1-2x)^-1 starts to expand to 1 + (-1)(-2x) + (-1)(-2)(-2x)^2 / 2! + ....
 
 
 
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