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I'm having a lot of trouble solving this integral. I can't seem to find any way to simplify it.

I tried to split the integral in two, but I couldn't find a way. I tried to find something that would let me have $\dfrac{f'(x)}{f(x)}$, but I had no luck.

Any hint?

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en.wikipedia.org/wiki/Elliptic_integral –  user114628 Jan 31 at 17:02

1 Answer 1

up vote 0 down vote accepted

The substitution $\frac{x^2-1}{x^2-4}=t^2$ will transform the integrand into a rational fraction.





$\frac {dx}{dt}=\frac{8t(t^2-1)-2t(4t^2-1)}{(t^2-1)^2}dt=\frac{10t}{(t^2-1)^2}dt$

Now the integral is $\int\frac{10 t^2}{(t^2-1)^2}dt$ and you can use partial fractions.

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If I substitute $ \frac{x^2-1}{x^2-4} $ with $ t^2 $ then calculating $ dt $ results in a hard-to-simplify derivative. I don't see how I could move on afterwards. Could you please show some extra steps? –  Vittorio Romeo Jan 31 at 17:10
Under that substitution, what is the relation between $dx$ and $dt$ so one could finish the substitution? –  coffeemath Jan 31 at 18:35
Може ли да ви отговоря на български? –  kmitov Jan 31 at 20:34
At the last step, you go from an expression for $x^2$ right to $dx/dt$. However the derivative of $x^2$ gives $2x(dx/dt)$ which is not what you have. –  coffeemath Feb 1 at 5:27

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