This page contains a complete infinite series exam with worked out solutions.
Each exam page contains a full exam with detailed solutions. Most of these are actual exams from previous semesters used in college courses. You may use these as practice problems or as practice exams. Here are some suggestions on how to use these to help you prepare for your exams.
- Set aside a chunk of full, uninterrupted time, usually an hour to two, to work each exam.
- Go to a quiet place where you will not be interrupted that duplicates your exam situation as closely as possible.
- Use the same materials that you are allowed in your exam (unless the instructions with these exams are more strict).
- Use your calculator as little as possible except for graphing and checking your calculations.
- Work the entire exam before checking any solutions.
- After checking your work, rework any problems you missed and go to the 17calculus page discussing the material to perfect your skills.
- Work as many practice exams as you have time for. This will give you practice in important techniques, experience in different types of exam problems that you may see on your own exam and help you understand the material better by showing you what you need to study.
IMPORTANT -
Exams can cover only so much material. Instructors will sometimes change exams from one semester to the next to adapt an exam to each class depending on how the class performs during the semester while they are learning the material. So just because you do well (or not) on these practice exams, does not necessarily mean you will do the same on your exam. Your instructor may ask completely different questions from these. That is why working lots of practice problems will prepare you better than working just one or two practice exams.
Calculus is not something that can be learned by reading. You have to work problems on your own and struggle through the material to really know calculus, do well on your exam and be able to use it in the future.
Okay, so here are a few videos we recommend that expand on the some of the above tips and also provide some insight on taking exams. This guy has lots of other videos about how to succeed in college, so we recommend his YouTube channel, Thomas Frank.
video by Thomas Frank |
---|
video by Thomas Frank |
---|
Recommended Books on Amazon (affiliate links) | ||
---|---|---|
![]() |
![]() |
![]() |
Exam Details | |
---|---|
Time | 1 hour |
Questions | 9 |
Total Points | 70 |
Tools | |
---|---|
Calculator | not allowed |
Formula Sheet(s) |
|
Other Tools | none |
Instructions: |
---|
- Show all your work. |
Note: Questions 1-8 are given below. Here is question 9.
Question 9 [5 points]
You must successfully* use each of these tests at least once in questions 1 - 8.
integral test |
ratio test |
root test |
divergence test |
direct comparison test |
limit comparison test |
*successfully means that the test proved either convergence or divergence;
- it does not count if the test was inconclusive;
- you must use all these tests to get any points on this question
Questions 1-8
Determine the convergence or divergence of these series. - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test listed above unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
\(\displaystyle{ \sum{ne^{-2n^2}} }\) (use the Integral Test)
Problem Statement |
---|
Determine the convergence or divergence of the series \(\displaystyle{ \sum{ne^{-2n^2}} }\) using the Integral Test. - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Final Answer |
---|
The series converges by the Integral Test.
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum{ne^{-2n^2}} }\) using the Integral Test. - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
For the integral test, we need determine where to determine the lower limit of integration after which the function will be decreasing and positive positive. To do this, we find the critical points.
\(\displaystyle{ f(x) = \frac{x}{e^{2x^2}} }\)
\( \begin{array}{rcl} f'(x) & = & \displaystyle{ \frac{e^{2x^2}(1) - x e^{2x^2}(4x)}{e^{4x^2}} } \\ & = & \displaystyle{ \frac{1-4x^2}{e^{2x^2}} } \end{array} \)
We used the quotient rule in the first line. The denominator of the result is always positive. So we only need to look at the numerator to determine where \(f'(x) = 0\).
\( 1-4x^2 = 0 \to x = \pm 1/2 \)
The largest critical value is \( +1/2 \), so let's choose \( 1 \) but first make sure that \(f(x)\) is positive and decreasing.
\(\displaystyle{ f'(1) = \frac{1-4}{e^2} = \frac{-3}{e^2} \lt 0 }\) So the function is decreasing since \(f'(x) < 0 \) for \( x > 1 \) and \(f(x)\) is positive. So we choose \(x = 1 \) as the lower limit of integration.
\(\int_{1}^{\infty}{ xe^{-2x^2} dx } = \lim_{b\to\infty}{ \int_{1}^{b}{ xe^{-2x^2} dx } }\)
This step is critical. The first integral cannot be evaluated since integration requires a finite interval. Since this is an improper integral, you must introduce the limit in order to integrate it.
Okay, for now, we will drop the limits of integration and evaluate the indefinite integral \(\int{ xe^{-2x^2} dx } \) Using substitution, we have \(\displaystyle{ u = -2x^2 \to du = -4xdx \to \frac{du}{-4} = xdx }\) our integral is now \(\int{ e^u \frac{du}{-4} = \frac{-1}{4}e^u = \frac{-1}{4}e^{-2x^2} }\) Now we will evaluate the definite integral \(\displaystyle{ \lim_{b\to\infty} \left[ \frac{-1}{4}e^{-2x^2} \right]_1^b = }\) \( \displaystyle{ \lim_{b\to\infty}\left[ \frac{-1}{4}e^{-2b^2} - \frac{-1}{4}e^{-2} \right] = }\) \(\displaystyle{ \frac{1}{4e^2} }\) which is finite, so the integral converges and therefore the series converges by the integral test.
Final Answer
The series converges by the Integral Test.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ 3 + \frac{5}{2} + \frac{7}{3} + \frac{9}{4} + . . . }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ 3 + \frac{5}{2} + \frac{7}{3} + \frac{9}{4} + . . . }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
\(\displaystyle{ 3 + \frac{5}{2} + \frac{7}{3} + \frac{9}{4} + . . . = }\) \(\displaystyle{ \sum_{n=1}^{\infty}{\frac{2n+1}{n} } }\)
\(\displaystyle{ \lim_{n\to\infty}{ \left[ \frac{2n+1}{n} \right] } = }\) \(\displaystyle{ \lim_{n\to\infty}\left[ 2 + \frac{1}{n} \right] = 2 }\). So the series diverges by the divergence test.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum{ \frac{2n+1}{n^2+n} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum{ \frac{2n+1}{n^2+n} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
Since the \(n^2\) term dominates all the other terms for large \(n\), we will compare this series to \(\sum{1/n}\), which is a divergent p-series. Both the Direct Comparison Test and the Limit Comparison Test work. First, let's use the Direct Comparison Test.
Let \(t_n = 1/n\) and \(a_n = (2n+1)/(n^2+n)\). Since the test series diverges, we need to set up the inequality \(0 \lt t_n \lt a_n \). The left inequality holds since \( 0 \lt t_n \). So we just need to show that \( t_n \lt a_n \) holds for some \(N\) where \( n \gt N\).
\(\begin{array}{rcl} \displaystyle{\frac{1}{n}} & < & \displaystyle{\frac{2n+1}{n^2+n}} \\ \displaystyle{\frac{n^2+n}{n}} & < & 2n + 1 \\ n+1 & < & 2n + 1 \\ n & < & 2n \\ 1 & < & 2 \end{array} \)
The last inequality is true for all \(n\). So the series diverges by the Direct Comparison Test with the divergent p-series \(\sum{1/n}\).
Using the Limit Comparison Test and using the same test series, \(t_n = \sum{1/n}\)
\(\begin{array}{rcl} \displaystyle{\lim_{n\to\infty}{\frac{a_n}{t_n}}} & = & \displaystyle{\lim_{n\to\infty}{\frac{2n+1}{n^2+n} \frac{n}{1}}} \\ & = & \displaystyle{\lim_{n\to\infty}{\frac{2n^2+n}{n^2+n}}} \\ & = & 2 \end{array}\)
Since \(\displaystyle{ \lim_{n\to\infty}{ \frac{a_n}{t_n}} = 2 \gt 0 }\), the series diverges by the Limit Comparison Test with the divergent p-series \( \sum{1/n} \).
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum_{n=2}^{\infty}{ \frac{2^{n+1}}{n^n} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum_{n=2}^{\infty}{ \frac{2^{n+1}}{n^n} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
\(\displaystyle{ \sum_{n=2}^{\infty}{ \frac{2^{n+1}}{n^n} } = 2 \sum_{n=2}^{\infty}{ \frac{2^{n}}{n^n} } }\)
Try the Root Test.
\( \begin{array}{rcl} \displaystyle{\lim_{n\to\infty}{ \sqrt[n]{ |a_n| } } } & = & \displaystyle{ \lim_{n\to\infty}{ \sqrt[n]{ \frac{2^n}{n^n} } } } \\ & = & \displaystyle{ \lim_{n\to\infty}{ \frac{2}{n} } } = 0 \end{array} \)
Since \( \displaystyle{\lim_{n\to\infty}{ \sqrt[n]{ |a_n| } } } < 1 \), the series converges by the Root Test.
Note: The Ratio Test also works.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{n^2}{e^n} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{n^2}{e^n} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
If we try the divergence test, we get zero. So the divergence test is indeterminate. Let's try the Ratio Test.
\( \begin{array}{rcl} \displaystyle{\lim_{n\to\infty}{ \left| \frac{a_{n+1}}{a_n} \right| }} & = & \displaystyle{\lim_{n\to\infty}{ \left[ \frac{(n+1)^2}{e^{n+1}} \cdot \frac{e^n}{n^2} \right] } } \\ & = & \displaystyle{\lim_{n\to\infty}{ \left[ \frac{(n+1)^2}{n^2} \cdot \frac{e^n}{e^{n+1}} \right] } } \\ & = & \displaystyle{ \lim_{n\to\infty}{ \left[ \left( 1 + \frac{1}{n} \right)^2 \cdot \frac{1}{e} \right] } = \frac{1}{e} } \end{array} \)
Since \( \displaystyle{\lim_{n\to\infty}{ \left| \frac{a_{n+1}}{a_n} \right| } = \frac{1}{e} < 1 }\), the series converges by the Ratio Test.
The Root Test also works as well as the Limit Comparison Test. The Direct Comparison Test might also work.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum_{n=2}^{\infty}{ \frac{1}{n(n+1)} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum_{n=2}^{\infty}{ \frac{1}{n(n+1)} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
Using partial fraction expansion, we have \(\displaystyle{ \frac{1}{n(n+1)} = \frac{1}{n} - \frac{1}{n+1} }\). If we build a table starting with \(n=2\), we get the partial sum \(\displaystyle{ S_n = \frac{1}{2} - \frac{1}{n+1} }\). Taking the limit as n approaches infinity, we get \(\displaystyle{ \lim_{n\to\infty}{S_n} = \frac{1}{2} }\). So the Telescoping Series converges to \(1/2\).
Note: You could have used other tests to prove convergence but you would have received only half the points since you would not have been able to determine what the series converges to.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{(-1)^{n+1}11^n}{n!} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{(-1)^{n+1}11^n}{n!} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
This is an alternating series, so we could use the alternating series to prove convergence or divergence. However, the instructions say that if we have positive and negative terms and the series converges, we need to determine if it converges conditionally or absolutely. So we will start by determing whether the series \(\displaystyle{ \sum{a_n} }\) converges or diverges.
We will use the Ratio Test since we have a factorial.
\(\begin{array}{rcl} \displaystyle{ \lim_{n\to\infty}{ \left| \frac{a_{n+1}}{a_n} \right| } } & = & \displaystyle{ \lim_{n\to\infty}{ \left| \frac{11^{n+1}}{(n+1)!} \cdot \frac{n!}{11^n} \right| } } \\ & = & \displaystyle{ \lim_{n\to\infty}{ \left| \frac{11}{n+1} \right| } = 0 } \end{array}\)
So the series converges by the Ratio Test. Since \( \sum{ |a_n| } \) converges, so does the series \(\sum{a_n}\) and it converges absolutely by the absolute convergence theorem.
The Root Test may also work.
Log in to rate this practice problem and to see it's current rating. |
---|
\(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{2^n}{e^{n+2}} } }\)
Problem Statement
Determine the convergence or divergence of the series \(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{2^n}{e^{n+2}} } }\). - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test that you studied unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.
Solution
\(\displaystyle{ \sum_{n=1}^{\infty}{ \frac{2^n}{e^{n+2}} } = }\) \(\displaystyle{ \frac{1}{e^2} \sum_{n=1}^{\infty}{ \frac{2^n}{e^n} } = }\) \(\displaystyle{ \frac{1}{e^2} \sum_{n=1}^{\infty}{ \left( \frac{2}{e} \right)^n } }\)
This is a geometric series with \( r = 2/e < 1 \).
We know a geometric series is \(\displaystyle{ \sum_{n=0}^{\infty}{r^n} = \frac{1}{1-r} }\). However, our series starts with one, not zero. So we can rewrite this as \(\displaystyle{ \sum_{n=1}^{\infty}{r^n} = \frac{1}{1-r} - 1 }\)
So this series converges to \(\displaystyle{ \frac{2e^{-2}}{e-2} }\).
Note: You could have used another test to prove convergence but you would not have been able to determine the value to which it converges. Done correctly, this would have given you 3 out of the 5 points.
Log in to rate this practice problem and to see it's current rating. |
---|
Really UNDERSTAND Calculus
Log in to rate this page and to see it's current rating.
all infinite series tests and topics |
To bookmark this page and practice problems, log in to your account or set up a free account.
Do you have a practice problem number but do not know on which page it is found? If so, enter the number below and click 'page' to go to the page on which it is found or click 'practice' to be taken to the practice problem.
| |
I recently started a Patreon account to help defray the expenses associated with this site. To keep this site free, please consider supporting me. |
---|
Support 17Calculus on Patreon |
|
---|
|
---|
Practice Instructions
Determine the convergence or divergence of these series. - If a series with positive and negative terms converges, state whether it converges conditionally or absolutely and show work supporting your answer.
- If possible, find the value that the series converges to.
- You may use any test listed above unless told to use a specific test.
- You may not use the idea of growth rate as your answer when evaluating limits.