What's wrong with this integral?
I'm trying to integrate (x)/(d+L-x) respect to x but I get -(d+L)ln(d+L-x) + d + L -x. The correct answer is -(d+L)ln(d+L-x) -x. What I did was to change the variable u = d + L -x. Then du= -dx. Also, x= d+L-u. Substituting I get ( -(d+L) +u)du/u. I divide the fraction in two, integrate and after substituting (d+L-x) back in u I don't get the correct answer. Any help is much appreciated.