Help evaluating $\int \frac{dx}{(x^2 + a^2)^2}$ I have following integral and it should be simple, however whatever substitution I use and no matter how many times I integrate it by parts (or combine both) I never get the correct solution (or any alternative solution):
$$\int \frac{dx}{(x^2 + a^2)^2}$$
I'm looking for what is on the Wolfram|Alpha in the alternative solutions section:
$$\frac{\arctan(\frac{x}{a})}{2a^3} + \frac{x}{2a^2(a^2 + x^2)} $$

$$\int\dfrac{1}{(x^2+a^2)^2}dx$$
Hint : Does there exist a function which when differentiated gives something similar to $1\over (x^2+1)$ ?
Put $\tan^{-1} \frac{x}{a} = t$. This gives $\dfrac{1}{1+(\dfrac{x}{a})^2}.\dfrac{1}{a}.dx = dt = \dfrac{a}{a^2+{x}^2}.dx$
$$\int\dfrac{1}{(x^2+a^2)^2}dx=\int \dfrac{1}{a.( (a\tan t)^2+a^2)}dt=\int \dfrac{1}{a.( a^2\tan^2 t+a^2)}dt=\int \dfrac{1}{a^3(\tan^2 t+1)}dt=\dfrac{1}{a^3}\int \cos^2 t$$
which will lead to the answer.
