5.1E: Exercises for Section 5.1

1.) State whether the given sums are equal or unequal.

1. and
2. and
3. and
4. and

Answer

a. They are equal; both represent the sum of the first 10 whole numbers.
b. They are equal; both represent the sum of the first 10 whole numbers.
c. They are equal by substituting
d. They are equal; the first sum factors the terms of the second.

In exercises 2 - 3, use the rules for sums of powers of integers to compute the sums.

2)

3)

Answer

Suppose that and .

In exercises 4 - 7, compute the sums.

4)

5)

Answer

6)

7)

Answer

In exercises 8 - 11, use summation properties and formulas to rewrite and evaluate the sums.

8)

9)

Answer

10)

11)

Answer

Let denote the left-endpoint sum using  subintervals and let denote the corresponding right-endpoint sum.

In exercises 12 - 19, compute the indicated left and right sums for the given functions on the indicated interval.

12) for on

13) for on

Answer

14) for on

15) for on

Answer

16) for on

17) for on

Answer

18) for on

19) for on

Answer

20) Compute the left and right Riemann sums— and , respectively—for on Compute their average value and compare it with the area under the graph of .

21) Compute the left and right Riemann sums— and , respectively—for on Compute their average value and compare it with the area under the graph of .

Answer

. The graph of is a triangle with area .

22) Compute the left and right Riemann sums— and , respectively—for on and compare their values.

23) Compute the left and right Riemann sums— and , respectively—for on and compare their values.

Answer

. They are equal.

For exercises 24 - 27, express the following endpoint sums in sigma notation but do not evaluate them.

24) for on

25) for on

Answer

26) for on

27) for on

Answer

In exercises 28 - 33, graph the function then use a calculator or a computer program to evaluate the following left and right endpoint sums. Is the area under the curve between the left and right endpoint sums?

28) [T] and for on the interval

29) [T] and for on the interval

Answer

The plot shows that the left Riemann sum is an underestimate because the function is increasing. Similarly, the right Riemann sum is an overestimate. The area lies between the left and right Riemann sums. Ten rectangles are shown for visual clarity. This behavior persists for more rectangles.

30) [T] and for on the interval

31) [T] and for on the interval

Answer

.
The left endpoint sum is an underestimate because the function is increasing. Similarly, a right endpoint approximation is an overestimate. The area lies between the left and right endpoint estimates.

32) [T] and for on the interval

33) [T] and for on the interval

Answer

.
The plot shows that the left Riemann sum is an underestimate because the function is increasing. Ten rectangles are shown for visual clarity. This behavior persists for more rectangles.

34) Let denote the time that it took Tejay van Garteren to ride the stage of the Tour de France in 2014. If there were a total of 21 stages, interpret .

35) Let denote the total rainfall in Portland on the day of the year in 2009. Interpret .

Answer

The sum represents the cumulative rainfall in January 2009.

36) Let denote the hours of daylight and denote the increase in the hours of daylight from day to day in Fargo, North Dakota, on the day of the year. Interpret

37) To help get in shape, Joe gets a new pair of running shoes. If Joe runs 1 mi each day in week 1 and adds mi to his daily routine each week, what is the total mileage on Joe’s shoes after 25 weeks?

Answer

The total mileage is mi.

38) The following table gives approximate values of the average annual atmospheric rate of increase in carbon dioxide (CO₂) each decade since 1960, in parts per million (ppm). Estimate the total increase in atmospheric CO₂ between 1964 and 2013.

Decade	Ppm/y
1964-1973	1.07
1976-1983	1.34
1984-1993	1.40
1994-2003	1.87
2004-2013	2.07

Average Annual Atmospheric CO2 Increase, 1964–2013 Source: http://www.esrl.noaa.gov/gmd/ccgg/trends/.

39) The following table gives the approximate increase in sea level in inches over 20 years starting in the given year. Estimate the net change in mean sea level from 1870 to 2010.

Starting Year	20- Year Change
1870	0.3
1890	1.5
1910	0.2
1930	2.8
1950	0.7
1970	1.1
1990	1.5

Approximate 20-Year Sea Level Increases, 1870–1990

Source: http://link.springer.com/article/10....712-011-9119-1

Answer

Add the numbers to get 8.1-in. net increase.

40) The following table gives the approximate increase in dollars in the average price of a gallon of gas per decade since 1950. If the average price of a gallon of gas in 2010 was $2.60, what was the average price of a gallon of gas in 1950?

Starting Year	10- Year Change
1950	0.03
1960	0.05
1970	0.86
1980	−0.03
1990	0.29
2000	1.12

Approximate 10-Year Gas Price Increases, 1950–2000

Source: epb.lbl.gov/homepages/Rick_Di...011-trends.pdf.

41) The following table gives the percent growth of the U.S. population beginning in July of the year indicated. If the U.S. population was 281,421,906 in July 2000, estimate the U.S. population in July 2010.

Year	% Change/Year
2000	1.12
2001	0.99
2002	0.93
2003	0.86
2004	0.93
2005	0.93
2006	0.97
2007	0.96
2008	0.95
2009	0.88

Annual Percentage Growth of U.S. Population, 2000–2009

Source: www.census.gov/popest/data.

(Hint: To obtain the population in July 2001, multiply the population in July 2000 by 1.0112 to get 284,573,831.)

Answer

309,389,957

In exercises 42 - 45, estimate the areas under the curves by computing the left Riemann sums, .

42)

43)

Answer

44)

45)

Answer

46) [T] Use a computer algebra system to compute the Riemann sum, , for for on

47) [T] Use a computer algebra system to compute the Riemann sum, , for for on

Answer

48) [T] Use a computer algebra system to compute the Riemann sum, , for for on . Compare these estimates with .

In exercises 49-50, use a calculator or a computer program to evaluate the endpoint sums and for . How do these estimates compare with the exact answers, which you can find via geometry?

49) [T] on the interval

Answer

By symmetry of the graph, the exact area is zero.

50) [T] on the interval

In exercises 51 - 52, use a calculator or a computer program to evaluate the endpoint sums and for .

51) [T] on the interval , which has an exact area of

Answer

52) [T] on the interval , which has an exact area of

53) Explain why, if and is increasing on , that the left endpoint estimate is a lower bound for the area below the graph of on

Answer

If is a subinterval of under one of the left-endpoint sum rectangles, then the area of the rectangle contributing to the left-endpoint estimate is . But, for , so the area under the graph of between and is plus the area below the graph of but above the horizontal line segment at height , which is positive. As this is true for each left-endpoint sum interval, it follows that the left Riemann sum is less than or equal to the area below the graph of on

54) Explain why, if and f is decreasing on that the left endpoint estimate is an upper bound for the area below the graph of on

55) Show that, in general,

Answer

and . The left sum has a term corresponding to and the right sum has a term corresponding to . In , any term corresponding to occurs once with a plus sign and once with a minus sign, so each such term cancels and one is left with

56) Explain why, if is increasing on , the error between either or and the area below the graph of is at most .

57) For each of the three graphs:

a. Obtain a lower bound for the area enclosed by the curve by adding the areas of the squares enclosed completely by the curve.

b. Obtain an upper bound for the area by adding to the areas of the squares enclosed partially by the curve.

Answer

Graph 1: a.
Graph 2:
Graph 3: a.

58) In the previous exercise, explain why gets no smaller while gets no larger as the squares are subdivided into four boxes of equal area.

59) A unit circle is made up of n wedges equivalent to the inner wedge in the figure. The base of the inner triangle is 1 unit and its height is The base of the outer triangle is and the height is . Use this information to argue that the area of a unit circle is equal to

Answer

Let be the area of the unit circle. The circle encloses congruent triangles each of area , so Similarly, the circle is contained inside congruent triangles each of area , so . As , so we conclude . Also, as , so we also have . By the squeeze theorem for limits, we conclude that