(a) Draw two typical curves y = f(x) and y = g(x), where f(x) > g(x) for a < x < b. Show how to approximate the area between these curves by a Riemann sum and sketch the corresponding approximating rectangles. Then write an expression for the exact area.
(b) Explain how the situation changes if the curves have equations x = f(y) and x = g(y), where f(y) > g(y) for c < y < d.