# Calculus 2 : Concepts of Convergence and Divergence

## Example Questions

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### Example Question #1 : Concepts Of Convergence And Divergence

One of the following infinite series CONVERGES. Which is it?  None of the others converge.   Explanation: converges due to the comparison test.

We start with the equation . Since for all values of k, we can multiply both side of the equation by the inequality and get for all values of k. Since is a convergent p-series with  hence also converges by the comparison test.

### Example Question #11 : Series In Calculus

Determine the nature of the following series having the general term:     The series is convergent.

The series is convergent.

Explanation:

We will use the Limit Comparison Test to show this result.

We first denote the genera term of the series by: and .

We have and the series have the same nature .

We know that is convergent by comparing the integral which we know is convergent.

Therefore by the Limit Comparison Test.

we have .

### Example Question #1 : Concepts Of Convergence And Divergence

If converges, which of the following statements must be true?

The limit of the term as approaches infinity is not zero.

None of the other answers must be true.

For some large value of  .

The limit of the partial sums as approaches infinity is zero.

For some large value of  .

Explanation:

If the series converges, then we know the terms must approach zero. At some point, the terms will be less than 1, meaning when you take the third power of the term, it will be less than the original term.

Other answers are not true for a convergent series by the term test for divergence.

In addition, the limit of the partial sums refers to the value the series converges to. A convergent series need not converge to zero. The alternating harmonic series is a good counter example to this.

### Example Question #21 : Series In Calculus

Which of following intervals of convergence cannot exist?

For any , the interval for some  For any such that , the interval   Explanation: cannot be an interval of convergence because a theorem states that a radius has to be either nonzero and finite, or infinite (which would imply that it has interval of convergence ). Thus, can never be an interval of convergence.

### Example Question #2 : Concepts Of Convergence And Divergence

Which of the following statements is true regarding the following infinite series? The series diverges, by the divergence test, because the limit of the sequence does not approach a value as The series diverges because for some and finite.

The series diverges to .

The series converges because The series diverges, by the divergence test, because the limit of the sequence does not approach a value as Explanation:

The divergence tests states for a series , if is either nonzero or does not exist, then the series diverges.

The limit does not exist, so therefore the series diverges.

### Example Question #3 : Concepts Of Convergence And Divergence

Determine whether the following series converges or diverges: The series conditionally converges.

The series diverges.

The series converges.

The series converges.

Explanation:

To prove the series converges, the following must be true:

If converges, then converges.

Now, we simply evaluate the limit: The shortcut that was used to evaluate the limit as n approaches infinity was that the coefficients of the highest powered term in numerator and denominator were divided.

The limit approaches a number (converges), so the series converges.

### Example Question #1 : Series Of Constants

Determine whether the following series converges or diverges. If it converges, what does it converge to?      Explanation:

First, we reduce the series into a simpler form. We know this series converges because By the Geometric Series Theorem, the sum of this series is given by ### Example Question #4 : Concepts Of Convergence And Divergence

Determine whether the following series converges or diverges. If it converges, what does it converge to?      Explanation:

Notice how this series can be rewritten as  Therefore this series diverges.

### Example Question #22 : Series In Calculus

There are 2 series, and , and they are both convergent. Is convergent, divergent, or inconclusive?

Inconclusive

Divergent

Convergent

Convergent

Explanation:

Infinite series can be added and subtracted with each other. Since the 2 series are convergent, the sum of the convergent infinite series is also convergent.

Note: The starting value, in this case n=1, must be the same before adding infinite series together.

### Example Question #1 : Sequences & Series

You have a divergent series , and you multiply it by a constant 10. Is the new series convergent or divergent?

Inconclusive

Divergent

Convergent

Divergent

Explanation:

This is a fundamental property of series.

For any constant c, if is convergent then is convergent, and if is divergent, is divergent. is divergent in the question, and the constant c is 10 in this case, so is also divergent.

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