1. The problem statement, all variables and given/known data prove by substitution that definite integral int (1/t)dt from [x to x*y] = int (1/t)dt from [1 to y]. 2. Relevant equations 3. The attempt at a solution i can do this problem if i integrate and use the log laws, no probs, but the question says to use a substitution, ive tried many but to no avail, a push in the right direction would be greatly appreciated. Ive asked yesterday about a similar question, which thanks to the forums help i understand. this is the last one on the section and then ill be confident that i can put it rest.