So I have an exam tomorrow, and the teacher provided a review. f(x) = ln(x + y) I remember that d/dx ln[f(x)] = f'(x)/f(x) so would that not equal 2/(x + y) ? The answer she gave is 1/(x + y - 1) ... where that neg. one came from I have no idea. Come to think of it, there were no problems on the homework that included two variables in this manner, so maybe the properties are slightly different? Also, find the derivative of sin(x)ln 3x... another problem that doesn't bear much resemblance to anything on the homework, a little confused on the order of operations here. I know that with something like 53x would be (3 ln 5)53x, so for this one, b = sin (x). Trying to replicate it the way the book would, (ln sin x)sin(x)ln 3x * (ln 3x)' the derivative of ln(3x) = 3/3x, bring that to the front and get ... I guess what I'm asking is do I use the general power rule or was I on the right track? At any point in time am I supposed to take the derivative of sin(x) and turn it into cos x?