I=[TEX]\int\limits_{0}^{1}(\frac{3}{x+1}-\frac{3}{(x+1)^2}+\frac{2ln(3x+1)}{(x+1)^2})dx[/TEX]
=I1+I2+I3
Xét I3 đặtu=2ln(3x+1) \Leftrightarrowdu=6dx/(3x+1)
dv=dx/(x+1)^2\Leftrightarrow v=-1/(x+1)
xét[TEX]\frac{1}{(3x+1)(x+1)}[/TEX]=[TEX]\frac{-1}{2(x+1)}[/TEX]+[TEX]\frac{3}{2(3x+1)}[/TEX]
\RightarrowI3=...