∫x1+x2 dx=\displaystyle\int \dfrac{x}{1 + x^2}\,dx =∫1+x2xdx=A11+x2+C\dfrac{1}{1 + x^2} + C1+x21+CBln(1+x2)+C\ln(1 + x^2) + Cln(1+x2)+CC12ln(1+x2)+C\dfrac{1}{2}\ln(1 + x^2) + C21ln(1+x2)+Ccheck_circleDarctanx+C\arctan x + Carctanx+CExplanationu=1+x2u = 1 + x^2u=1+x2, du=2x dxdu = 2x\,dxdu=2xdx. ∫(1/u)du/2=ln∣u∣/2\int (1/u) du/2 = \ln|u|/2∫(1/u)du/2=ln∣u∣/2.