SOLUTION: Note that the subinterval widths are not equal.
(a) In each subinterval, we sketch the rectangle with height determined by the point on f at the
left end-point. Our estimate is the sum of the areas of these rectangles:
A ≈ 1(7) + 3(11) + 2(13) + 4(12) ≈ 114(b) In each subinterval, we sketch trapezoids by drawing segments connecting the points on f.
Our estimate is the sum of the areas of these trapezoids:Comparing Approximating Sums