Calculus 2 : Ratio Test

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #101 : Ratio Test

Determine the convergence or divergence of the following series:

Possible Answers:

The series is divergent

The series is convergent

The series is conditionally convergent

The series may conditionally convergent, divergent, or absolutely convergent.

Correct answer:

The series is divergent

Explanation:

To determine the convergence or divergence of the following series, we must use the Ratio Test, which states that for the series , and , that when , the series diverges, when , the series converges, and when , the series may be absolutely convergent, conditionally convergent, or divergent.

For our series, using the above formula, we get 

which simplified becomes

Note that the factorial was simplified by rewriting .

In the limit, the n in the numerator goes to infinity, which makes L go to infinity, which is greater than 1. Thus, the series diverges.

Example Question #102 : Ratio Test

Determine if the series converges or diverges:

Possible Answers:

The series diverges

The series converges

The series may absolutely converge, conditionally converge, or diverge

The series conditionally converges

Correct answer:

The series converges

Explanation:

To determine the convergence or divergence of the series, we must use the ratio test, which states that for a given series , and , if L is greater than 1, the series diverges, if less than 1, the series converges, and if L is equal to 1, the series may absolutely converge, conditionally converge, or diverge.

Now, we must find L:

We simplified the limit using the properties of radicals and exponents. The denominator of the limit becomes infinitely large, so the term goes to zero. L is therefore less than 1, so the series converges. 

Example Question #101 : Ratio Test

Determine if the series converges (absolutely or conditionally) or diverges:

Possible Answers:

May Absolutely or Conditionally converge, or diverge. 

Conditionally Converges

Absolutely Converges

Diverges

Correct answer:

Absolutely Converges

Explanation:

Using the ratio test , we get . Evaluating the limit, we get . Because  the series converges. Also, because no n value could make the series negative, it absolutely converges . 

Example Question #101 : Ratio Test

Determine whether the series converges or diverges:

Possible Answers:

Conditionally Converges

Absolutely Converges

Diverges

May converge or diverge

Correct answer:

Diverges

Explanation:

Using the ratio test, we get  and therefore, the series diverges. We simplify the inside by saying  and that  which cancels out with the denominator. 

Example Question #103 : Ratio Test

Does the series converge?

Possible Answers:

Converges in an interval

Does not converge

Converges conditionally

Converges

Correct answer:

Converges

Explanation:

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Example Question #2921 : Calculus Ii

Does the following series converge or diverge?

Possible Answers:

Converge

Diverge

Correct answer:

Diverge

Explanation:

To determine the convergence or divergence of the series, the most apparent way to do so is by using the ratio test. The ratio test states that a series will converge if:

The series will diverge if:

 

The ratio test can be used by first writing all n as n+1 in the numerator and the denominator is the normal series:

This simplifies to:

Because the limit is larger than one, the series diverges. 

Example Question #107 : Ratio Test

Does the following series converge or diverge?

Possible Answers:

Conditionally converge

Diverge

Absolutely converge

The series either diverges, absolutely converges, or conditionally converges.

Correct answer:

Diverge

Explanation:

To determine the convergence or divergence of the series, the most apparent way to do so is by using the ratio test. The ratio test states that a series will converge if:

The series will diverge if:

 

The ratio test can be used by first writing all n as n+1 in the numerator and the denominator is the normal series:

This simplifies to:

Because the limit is larger than one, the series diverges. 

Example Question #105 : Ratio Test

Use limit ratio test for positive series to determine if the following series diverges or converges:

Possible Answers:

Converges

Diverges

Correct answer:

Converges

Explanation:

Consider the following limit:

Therefore, 

   

Then, according to limit ratio test for positive series:

K=1, therefore both  converge or diverge.

We know, that  is generalized harmonic series with p=3, therefore it converges. Consecutively, by limit ratio test,  also converges.

Example Question #109 : Ratio Test

Compute the limit  to determine if the series

  converges or diverges using the ratio test. 

 

 

 



Possible Answers:

The series is absolutely convergent, and therefore converges.  

L = 2/3

The series diverges. 

L = 2/3

The series diverges. 

L = 1/9 

The series may be divergent, conditionally convergent, or absolutely convergent. 

L = 1

The series is absolutely convergent, and therefore converges. 

L = 1/9 

Correct answer:

The series is absolutely convergent, and therefore converges. 

L = 1/9 

Explanation:

Compute the limit  to determine if the series

  converges or diverges, or neither. 

 

 

 

______________________________________________________________

Define for the sequence  the limit  . The ratio test states:

the series  

If  then the series  converges absolutely, and therefore converges. 

If  then the series  diverges. 

 

If  then the series  either converges absolutely, is divergent, or conditionally convergent. 

________________________________________________________________

 

 

 

 

 

 

 

To write the numerator in the limit we need to compute, note that every  will become  which simplifies down to . So we have for 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Because  we can conclude that the series  converges by the ratio test. 

 

 

 

Example Question #102 : Ratio Test

Find the interval of convergence of the following series

Possible Answers:

Correct answer:

Explanation:

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