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    I have a problem with understanding the point of the second part of the question. How to get an expansion of f(x) when it can go on forever? If I get an expression taking just till the coefficient of x^3 then it's a meaningless expression, and is incomplete?
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    you will get two separate expansions, one for each of the underneath brackets... select the terms in each up to x3 and combine them together.
    as you say the whole expansion will be infinite but just keeping the low powers is very useful.
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    If you are pedantic, put "..." after the expansions to indicate they continue

    For example

    (1-x)^-1



1 + x + x^2 + ...
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    (Original post by bmqib)
    Name:  0-magemf.png
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    I have a problem with understanding the point of the second part of the question. How to get an expansion of f(x) when it can go on forever? If I get an expression taking just till the coefficient of x^3 then it's a meaningless expression, and is incomplete?
    It is not meaningless

    Since |x|<1 the higher powers of x are very small values

    Therefore a small number of terms will give a good approximation
 
 
 
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