(B) Use areas; then . Thus, f (7) −f (1) = 7.(B) The region x units from the stage can be approximated by the
semicircular ring shown; its area is then the product of its circumference
and its width.The number of people standing in the region is the product of the area
and the density:To find the total number of people, evaluate(B) is positive, but decreasing; hence .(C)(E) On 2 ≤ t ≤ 5, the object moved ft to the right; then on 5 t 8, it
moved only ft to the left.