So let's review what we're doing when we take just a regular definite integral. So if we take the definite integral between say 0 and 2 of x squared dx, what does that represent? Let's look at our endpoints. So this is x is equal to 0. Let's say that this right over here is x is equal to 2. What we're doing is for each x we're finding a little dx around it. So this right over here is a little dx.