The document discusses various methods for approximating the area under a curve including: - Left, right, and midpoint rectangular approximation methods which divide the area into rectangles to estimate it - Area methods involving integrating curves bounded by the x-axis, y-axis, or between two curves - Volume methods like the disk, washer, and shell methods that revolve curves around axes to find volumes and relate to areas It concludes that the rectangular approximation methods are used to estimate areas by dividing them into rectangles, and that the midpoint method provides the most accurate approximation.