y is equal to f of x, which is equal to x. And now let me graph the derivative, let me graph f prime of x. That's saying it's 1, that's saying it's 1 for all x, regardless of what x is, it's going to be equal to 1. Is this consistent with what we know about derivatives and slopes and all the rest? Well, let's look at our function. What is the slope of the line, or the tangent line, right at this point? Well, the slope of this right over here, this has slope 1 continuously, or it has a constant slope of 1.