This is what delta x is right now. It's this distance. But if delta x got a little bit smaller, then it would start, the secant line would look like that. Got even smaller, the secant line would look like that. It gets even smaller, then we're getting pretty close to the slope of the tangent line. The tangent line is this thing right here that I want to find the slope of. So let's find the limit as our delta x approaches 0.