We'll use that same shade. It is f of x sub n minus 1 times delta x. And we're done. We've written it in a very general way. But to really make us comfortable with the various forms of notation, especially the types of notation you might see when people are talking about approximating areas or sums in general, I'm going to use the traditional sigma notation. So another way we could write this as the sum. This is equal to the sum from, and remember, this is just based on the conventions that I set up.