So let's just say you wanted to find a sum of some terms. And these terms have a pattern. So let's say you want to find a sum of the first 10 numbers. You could say 1 plus 2 plus 3 plus, and you go all the way to plus 9 plus 10. And I clearly could have even written this whole thing out. But you can imagine it becomes a lot harder if you wanted to find the sum of the first 100 numbers. So that would be 1 plus 2 plus 3 plus, and you would go all the way to 99 plus 100.