\(=\dfrac{1}{2}\int \dfrac{x^2}{(x^2+1)^3}d(x^2+1)\)
\(=\dfrac{1}{2}\int \dfrac{x^2+1}{(x^2+1)^3}d(x^2+1)-\dfrac{1}{2}\int \dfrac{1}{(x^2+1)^3}d(x^2+1)\)
\(=\dfrac{1}{2}\int \dfrac{1}{(x^2+1)^2}d(x^2+1)-\dfrac{1}{2}\int \dfrac{1}{(x^2+1)^3}d(x^2+1)\)
\(=-\dfrac{1}{2}.\dfrac{1}{x^2+1}+\dfrac{1}{4}.\dfrac{1}{(x^2+1)^2}\)