Well as delta x approaches 0, this is just going to be equal to x. So if this approaches x as delta x approaches 0, and it's less than this function, and if this approaches x as delta x approaches 0, and it's always greater than this, then we know from the squeeze theorem or the sandwich theorem that the limit as delta x approaches 0 of c as a function of delta x is going to be equal to x as well. It has to approach the same thing that that and that is. It's sandwiched in between. And so that's a slight, we resort to the sandwich theorem. It's a little bit more rigorous to get to this exact result. As delta x approaches 0, c approaches x.