Find the integral $\int \frac{dx}{(x+a)^2(x+b)^2}$

Question

Find THE integral

$\int \frac{dx}{(x+a)^2(x+b)^2}$

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My question is when multiply by $(x+a)^2(x+b)^2$ we assume that $x$ $\neq$ to $-a$ and $-b$.How then we can put $-a$ for $x$.