Using rectangles whose height is given by the value of the function at the midpoint of the rectangle's base, estimate the area under the graph using first two and then four rectangles. f(x) =x- between x= 1 and x = 3 Using two rectangles to estimate, the area under f(x) is approximately (Type an integer or a simplified fraction.) Using four rectangles to estimate, the area under f(x) is approximately (Type an integer or a simplified fraction.)