My function looks like this, at least in the first quadrant. That's where I'll graph it for now. I could also graph it, obviously, in the second quadrant. But what I care about is the area under this curve and above the positive x axis between x equals 1 and x equals 4. And I'm tired of approximating areas. I want to find the exact area under this curve, above the x axis. And the way we denote the exact area under the curve, this little brown shaded area, is using the definite integral.