This is a notation for limits. So we're going to use our limit as H approaches zero of t + H / 7 * t + H + 2 - t / 7 T +2 all over H So the limit as H approaches zero of t + H * 7 T plus 2 - t times the quantity seven t + 7 H +2. Just getting a common denominator here over seven t + H + 2 times 7 T +2 and I'm going to bring that H into the denominator where it's common. Then we're going to distribute foil, combine like terms, cancel, etcetera. So the limit as H goes to zero of seven t ^2 + 2 T, +7 TH +2 H minus seven t ^2 -, 7 TH -2 T Remember that everything without an H net better cancel it this step. If it doesn't, we have truly done something wrong. So when I look here, here's a +2 T and a -2 T, here's a +7 T squared and a -7 T squared, and all the other terms have a single H in them. So we're going to factor out that H and cancel it with the H in the denominator. So I'm going to end up with seven T + 2 - 7 T all over seven T + H plus 2 * 7 T +2 when I put H going to 0. Now we're going to get two over, oops, These terms back here cancelled, but it didn't matter because they had an H in them, so I just cancelled them now. So we get 2 / 7 T +2. Wow. Seven t + 2 quantity squared.