On this problem, we need to figure out what our F of X + H is. Well, whenever we have F of anything in the parenthesis, it means that when we see our unknown, we're going to put in whatever is in the parenthesis. So our F of X + H is just 5 / X + H Our F of X is just 5 / X. Now if that seems a little foreign, what I recommend is to go back and do some numbers. If I asked you for F of one, you would tell me 5 / 1 or five. If I asked you for F of -7, you would say 5 / -7. If I asked you for F of A, you would tell me 5 / A. So if I ask you for F of X + H, hopefully you say 5 / X + H So going back to the original problem, we now need to put in 5 / X + H -, 5 / X all over H So our first step is to get a common denominator, and that's going to be X * X + H for the numerator of this complex fraction. So we're going to have 5 * X minus. Maybe I should do it in a few more steps. 5 * X and then we'll -5 * X + H over the X * X + H and that's all divided by the H. So if we distribute, we'd get five X -, 5 X -5 H over X * X + H all divided by H The five XS are going to cancel, so we get -5 H over X * X + H and if we divide by H, that's the really the same thing as multiplying by 1 / H The HS are going to cancel and we get -5 / X * X + H.