Let I=∫2x−1x+1dx Put 2x−1=t $\begin{array}{l}
\therefore \quad 2 x-1=t^{2} \Rightarrow d x=t d t \
I=\int \frac{\left(t^{2}+3\right)}{2} d t=\frac{t^{3}}{6}+\frac{3 t}{2}+C \
=\frac{(2 x-1)^{\frac{3}{2}}}{6}+\frac{3}{2}(2 x-1)^{\frac{1}{2}}+C \
=\sqrt{2 x-1}\left(\frac{x+4}{3}\right)+C \
=f(x) \cdot \sqrt{2 x-1}+C
\end{array}Hence,f(x)=\frac{x+4}{3}$