Limit as delta x approaches 0. I'm just rewriting what I have here. So I said the square root of x plus delta x minus square root of x, all of that over delta x. And I'm going to multiply that, after switching colors, times square root of x plus delta x plus the square root of x over the square root of x plus delta x plus the square root of x, right? This is just 1. So I could, of course, multiply that times, if we assume that x and delta x aren't both 0, this is a defined number. This would be 1.