to integrate (1/k)/(1 - y/k), do a substitution: u = 1 - y/k

now continue with that and see where you get. and try to notice a pattern so that you don't have to go through the u-sub all the time. and remember that in general, to integrate 1/something, you don't automatically take the ln|something|, it very much depends on the kind of function "something" is. follow the rules exactly. you have . If it doesn't (or can't) look like 1/x (that is one over a variable to the first degree), then you won't be able to integrate it and get ln. what you have doesn't look like 1/x, so you had to change it to look like that. And that would change other things as well.