Integration by Reduction Formulae

saladfinger16
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Can anyone help me out with a proof for the integral that's in the attached images, its driving me nuts :frown:
 

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You could try the trig substitution x = a*tan(u).

Or note that

\int\frac{dx}{(x^2 + a^2)^n} = \int\frac{dx}{(x^2 + a^2)^{n-1}} - \int\frac{x^2 + a^2 - 1}{(x^2 + a^2)^n}\,dx

and try to work out the last integral on the right.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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