And let me graph y equals x. So y is equal to f of x here, so y is equal to x. So it looks something like that. So y is equal to x, or this is f of x equals to x, or y is equal to this f of x right over there. Now, the derivative, actually let me just call that f of x, just to make it, not to confuse you. So this right over here is f of x is equal to x that I graphed right over here. y is equal to f of x, which is equal to x.