Your first step into calculus — measuring areas, distances, and totals
You already know how to find the area of a rectangle: length × width. But what about the area under a curve? That's the big question that calculus was invented to answer — and it's called integration.
The trick: fill the curved area with rectangles you can measure, and add them up. The more rectangles, the closer to the true area. This idea — the Riemann sum — is how integrals work under the hood.
In this lesson, you'll build rectangles under y = 4 - x^2, watch the approximation improve as you add more, and discover why integrals matter everywhere — from physics (distance from speed) to economics (total revenue from a rate).