jacks said:
$(1)\displaystyle \;\; \int\frac{1}{1+x^6}dx$
$(2)\displaystyle \;\; \int\frac{1}{1+x^8}dx$
May be is useful to consider the general case...
$\displaystyle \int \frac{dx}{1+x^{n}}$ (1)
The root of the polinomial $\displaystyle 1+x^{n}$ are $\displaystyle x_{k}= e^{i\ \frac{2k+1}{n}\ \pi}\ ,\ k= 0.1,...,n-1$ so that is...
$\displaystyle \frac{1}{1+x^{n}} = \sum_{k=0}^{n-1} \frac{r_{k}}{x-x_{k}}$ (2)
... where...
$\displaystyle r_{k}= \lim_{x \rightarrow x_{k}} \frac{x-x_{k}}{1+x^{n}}$ (3)
Now You can integrate (2) 'term by term' obtaining... $\displaystyle \int \frac{dx}{1+x^{n}}= \sum_{k=0}^{n-1} r_{k}\ \ln (x-x_{k}) + c $ (4)
Kind regards
$\chi$ $\sigma$
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