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I find trouble in calculating the following integral:

$$ \int_0^R \frac{m\cdot x}{m+s\cdot x^a} \,dx $$

Mathematica does not provide an output for this function, however, there seems to be an output in the online http://integrals.wolfram.com/ tool for an upper limit to infinity. The result given in this tool is as follows: online integration

Any suggestions on the computation of this integral? Perhaps any suggestions for approximating the integral under specific assumptions for the values of m, s, a or R..

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  • $\begingroup$ If $a$ is an integer, you should be able to do it by using partial fractions. $\endgroup$ – Raskolnikov Apr 24 '13 at 7:45
  • $\begingroup$ Since you're interested in an approximation, what are the relative sizes of $m,s,a,R$? $\endgroup$ – Antonio Vargas Apr 24 '13 at 15:12
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I am thinking that since the indefinite integral of this function equals to

$$ F(x)=\int \frac{m\cdot x}{m+s\cdot x^a} \,dx=x^2*\,_2F_1[1, 2/a, 1 + 2/a, -sx^a/m]/2 $$

Then, by taking F(R)-F(0) we get the result of the definite integral. Any remarks?

Result: $$ \int_0^R \frac{m\cdot x}{m+s\cdot x^a} \,dx=F(R)-F(0)=R^2*\,_2F_1[1, 2/a, 1 + 2/a, -sR^a/m]/2 $$

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  • $\begingroup$ Once you have the indefinite integral, the next step is fine. $\endgroup$ – Ross Millikan Apr 26 '13 at 17:28

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