Calculus 2 : Riemann Sums

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #1 : Riemann Sums

Find the Left Riemann sum of the function

\displaystyle f(x)=x+7

on the interval \displaystyle [0,8] divided into four sub-intervals.

Possible Answers:

\displaystyle 60

\displaystyle 100

\displaystyle 80

\displaystyle 40

Correct answer:

\displaystyle 80

Explanation:

The interval \displaystyle [0, 8] divided into four sub-intervals gives rectangles with vertices of the bases at

\displaystyle x=0,2,4,6,8

For the Left Riemann sum, we need to find the rectangle heights which values come from the left-most function value of each sub-interval, or f(0), f(2), f(4), and f(6).

\displaystyle f(0) = 0+7 = 7

\displaystyle f(2) = 2+7 = 9

\displaystyle f(4) = 4+7 = 11

\displaystyle f(6) = 6+7 = 13

Because each sub-interval has a width of 2, the Left Riemann sum is

\displaystyle A = bh = 2(7+9+11+13) = 80

Example Question #1 : Integrals

Given a function \displaystyle y=x^{2}, find the Left Riemann Sum of the function on the interval \displaystyle [0,6] divided into three sub-intervals. 

Possible Answers:

\displaystyle 44

\displaystyle 36

\displaystyle 38

\displaystyle 42

\displaystyle 40

Correct answer:

\displaystyle 40

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,6] divided into \displaystyle 3 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,2,4,6

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=2 because the rectangles are spaced \displaystyle 2 units apart. Since we're looking for the Left Riemann Sum, we want to find the heights \displaystyle h of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=(0)^{2}=0

\displaystyle f(2)=(2)^{2}=4

\displaystyle f(4)=(4)^{2}=16

Putting it all together, the Left Riemann Sum is 

\displaystyle A=bh=2(0+4+16)=2(20)=40.

Example Question #1 : Riemann Sums

Given a function \displaystyle y=\frac{1}{4}x+2, find the Left Riemann Sum of the function on the interval \displaystyle [0,4] divided into four sub-intervals. 

Possible Answers:

\displaystyle \frac{25}{2}

\displaystyle \frac{17}{2}

\displaystyle \frac{19}{2}

\displaystyle \frac{23}{2}

\displaystyle \frac{21}{2}

Correct answer:

\displaystyle \frac{19}{2}

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,4] divided into \displaystyle 4 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3,4

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 unit apart. Since we're looking for the Left Riemann Sum, we want to find the heights \displaystyle h of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=\frac{1}{4}(0)+2=0+2=2

\displaystyle f(1)=\frac{1}{4}(1)+2=\frac{1}{4}+\frac{8}{4}=\frac{9}{4}

\displaystyle f(2)=\frac{1}{4}(2)+2=\frac{1}{2}+\frac{4}{2}=\frac{5}{2}

\displaystyle f(3)=\frac{1}{4}(3)+2=\frac{3}{4}+\frac{8}{4}=\frac{11}{4}

Putting it all together, the Left Riemann Sum is 

\displaystyle A=bh=1(2+\frac{9}{4}+\frac{5}{2}+\frac{11}{4})=\frac{8}{4}+\frac{9}{4}+\frac{10}{4}+\frac{11}{4}=\frac{38}{4}=\frac{19}{2}

Example Question #53 : Integrals

Given a function \displaystyle y=3x, find the Left Riemann Sum of the function on the interval \displaystyle [0,3] divided into three sub-intervals. 

Possible Answers:

\displaystyle 6

\displaystyle 10

\displaystyle 8

\displaystyle 7

\displaystyle 9

Correct answer:

\displaystyle 9

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,3] divided into \displaystyle 3 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 unit apart. Since we're looking for the Left Riemann Sum, we want to find the heights \displaystyle h of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=3(0)=0

\displaystyle f(1)=3(1)=3

\displaystyle f(2)=3(2)=6

Putting it all together, the Left Riemann Sum is 

\displaystyle A=bh=1(0+3+6)=9

Example Question #54 : Integrals

Given a function \displaystyle y=\frac{1}{2}x^{2}, find the Left Riemann Sum of the function on the interval \displaystyle [0,8] divided into four sub-intervals.

Possible Answers:

\displaystyle 58

\displaystyle 56

\displaystyle 52

\displaystyle 54

\displaystyle 50

Correct answer:

\displaystyle 56

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,8] divided into \displaystyle 4 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,2,4,6,8.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is because the rectangles are spaced units apart. Since we're looking for the Left Riemann Sum, we want to find the heights of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=\frac{1}{2}(0)^{2}=0

\displaystyle f(2)=\frac{1}{2}(2)^{2}=2

\displaystyle f(4)=\frac{1}{2}(4)^{2}=8

\displaystyle f(6)=\frac{1}{2}(6)^{2}=18

Putting it all together, the Left Riemann Sum is

\displaystyle A=bh=2(0+2+8+18)=2(28)=56.

Example Question #55 : Integrals

Given a function \displaystyle y=3x+6, find the Left Riemann Sum of the function on the interval \displaystyle [0,3] divided into three sub-intervals.

Possible Answers:

\displaystyle 23

\displaystyle 21

\displaystyle 25

\displaystyle 27

\displaystyle 19

Correct answer:

\displaystyle 27

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval  \displaystyle [0,3] divided into \displaystyle 3 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 unit apart. Since we're looking for the Left Riemann Sum, we want to find the heights  of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=3(0)+6=0+6=6

\displaystyle f(1)=3(1)+6=3+6=9

\displaystyle f(2)=3(2)+6=6+6=12

Putting it all together, the Left Riemann Sum is

\displaystyle A=bh=1(6+9+12)=15+12=27.

Example Question #1 : Riemann Sums

Given a function \displaystyle y=\frac{5}{x}, find the Right Riemann Sum of the function on the interval \displaystyle [0,4] divided into four sub-intervals.

Possible Answers:

\displaystyle \frac{124}{12}

\displaystyle \frac{125}{12}

\displaystyle \frac{123}{12}

\displaystyle \frac{126}{12}

\displaystyle \frac{122}{12}

Correct answer:

\displaystyle \frac{125}{12}

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval  \displaystyle [0,4] divided into \displaystyle 4 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3,4.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 unit apart. Since we're looking for the Right Riemann Sum of \displaystyle y=\frac{5}{x}, we want to find the heights  of each rectangle by taking the values of each rightmost function value on each sub-interval, as follows:

\displaystyle f(4)=\frac{5}{4}

\displaystyle f(3)=\frac{5}{3}

\displaystyle f(2)=\frac{5}{2}

\displaystyle f(1)=\frac{5}{1}=5

Putting it all together, the Right Riemann Sum is

\displaystyle A=bh=1(\frac{5}{4}+\frac{5}{3}+\frac{5}{2}+5)=\frac{15}{12}+\frac{20}{12}+\frac{30}{12}+\frac{60}{12}=\frac{125}{12}.

Example Question #57 : Integrals

Given a function \displaystyle y=x^{3}, find the Left Riemann Sum of the function on the interval \displaystyle [0,4] divided into four sub-intervals.

Possible Answers:

\displaystyle 36

\displaystyle 38

\displaystyle 44

\displaystyle 40

\displaystyle 42

Correct answer:

\displaystyle 36

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,4] divided into \displaystyle 4 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3,4.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 units apart. Since we're looking for the Left Riemann Sum, we want to find the heights of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=(0)^{3}=0

\displaystyle f(1)=(1)^{3}=1

\displaystyle f(2)=(2)^{3}=8

\displaystyle f(3)=(3)^{3}=27

Putting it all together, the Left Riemann Sum is

\displaystyle A=bh=1(0+1+8+27)=36.

Example Question #58 : Integrals

Given a function \displaystyle y=\frac{x^{2}}{2}, find the Left Riemann Sum of the function on the interval \displaystyle [0,3]  divided into three sub-intervals.

Possible Answers:

\displaystyle \frac{11}{2}

\displaystyle \frac{5}{2}

\displaystyle \frac{3}{2}

\displaystyle \frac{7}{2}

\displaystyle \frac{9}{2}

Correct answer:

\displaystyle \frac{5}{2}

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [0,3] divided into \displaystyle 3 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=0,1,2,3.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 units apart. Since we're looking for the Left Riemann Sum, we want to find the heights  of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(0)=\frac{(0)^{2}}{2}=0

\displaystyle f(1)=\frac{(1)^{2}}{2}=\frac{1}{2}

\displaystyle f(2)=\frac{(2)^{2}}{2}=\frac{4}{2}=2

Putting it all together, the Left Riemann Sum is

\displaystyle A=bh=1(0+\frac{1}{2}+2)=\frac{5}{2}.

Example Question #1 : Riemann Sums

Given a function \displaystyle y=\frac{2}{x}, find the Left Riemann Sum of the function on the interval \displaystyle [1,4]  divided into three sub-intervals.

Possible Answers:

\displaystyle 5

\displaystyle \frac{17}{3}

\displaystyle \frac{13}{3}

\displaystyle \frac{11}{3}

\displaystyle 3

Correct answer:

\displaystyle \frac{11}{3}

Explanation:

In order to find the Riemann Sum of a given function, we need to approximate the area under the line or curve resulting from the function using rectangles spaced along equal sub-intervals of a given interval. Since we have an interval \displaystyle [1,4] divided into \displaystyle 3 sub-intervals, we'll be using rectangles with vertices at \displaystyle x=1,2,3,4.

To approximate the area under the curve, we need to find the areas of each rectangle in the sub-intervals. We already know the width or base of each rectangle is \displaystyle b=1 because the rectangles are spaced \displaystyle 1 units apart. Since we're looking for the Left Riemann Sum, we want to find the heights  of each rectangle by taking the values of each leftmost function value on each sub-interval, as follows:

\displaystyle f(1)=\frac{2}{1}=2

\displaystyle f(2)=\frac{2}{2}=1

\displaystyle f(3)=\frac{2}{3}

Putting it all together, the Left Riemann Sum is

\displaystyle A=bh=1(2+1+\frac{2}{3})=3+\frac{2}{3}=\frac{9}{3}+\frac{2}{3}=\frac{11}{3}.

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