# Calculus 2 : Arithmetic and Geometric Series

## Example Questions

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### Example Question #1 : Arithmetic And Geometric Series

How many terms of a geometric series must you know in order to uniquely define that series?

Four

One

Five

Two

Three

Two

Explanation:

In order to uniquely define the geometric series, we need to know two things: the ratio between successive terms and at least one of the terms. Knowing one term doesn't give you the ratio of successive terms, but knowing two terms will give you the ratio. By the term generator for a geometric series , you can see that you only need two terms to find the ratio

### Example Question #1 : Arithmetic And Geometric Series

Assume the term generator for an arithmetic sequence is . What is the sum of the first  terms of this sequence ?

Explanation:

The sum formula for  terms of an arithmetic series is .

For  terms, this formula becomes .

Using our term generator for  and , this formula becomes

.

### Example Question #6 : Types Of Series

What value does the series  approach?

Explanation:

We can evaluate the infinite series by recognizing it as a geometric series times some constant.

Let's manipulate this series:

.

Now it suffices to evaluate , which we can recognize as the power series of  with , which is

.

So we have

.

### Example Question #7 : Types Of Series

Determine whether the series is arithmetic. If so, find the common difference.

Series is not arithmetic

Series is not arithmetic

Explanation:

If a series is arithmetic, then there exists a common difference between each pair of consecutive terms in the series.

For this series

Because

and

we find that there does NOT exist a common difference and as such,

the series is not arithmetic.

### Example Question #8 : Types Of Series

Determine whether or not the geometric series converges. If it converges, find the sum of the sequence.

Series does not converge.

Series does not converge.

Explanation:

To determine the convergency of a geometric series, we must find the absolute value of the common ratio.

A geometric series will converge if the absolute value of the common ratio is less than one, or

In this problem, we see that

And because

we conclude that the series does not converge to a finite sum.

### Example Question #9 : Types Of Series

Calculate the sum of the following series:

Explanation:

This is an arithmetic series.

Its general form is .

To calculate the sum of very large series such as these, use the formula

This works because you are taking the average of the largest and smallest terms, and then multiplying them by n, which is the same as calculating the sum total.

Solution:

### Example Question #2 : Arithmetic And Geometric Series

Calculate the sum of the following series:

Explanation:

This is an arithmetic series.

Its general form is

To calculate the sum of very large series such as these, use the formula

This works because you are taking the average of the largest and smallest terms, and then multiplying them by n, which is the same as calculating the sum total.

Solution:

### Example Question #3 : Arithmetic And Geometric Series

Calculate the sum of the following series:

Explanation:

This is an arithmetic series.

Its general form is

To calculate the sum of very large series such as these, use the formula

This works because you are taking the average of the largest and smallest terms, and then multiplying them by n, which is the same as calculating the sum total.

Solution:

### Example Question #4 : Arithmetic And Geometric Series

Calculate the sum of the following series:

Explanation:

This is an arithmetic series.

Its general form is

To calculate the sum of very large series such as these, use the formula

This works because you are taking the average of the largest and smallest terms, and then multiplying them by n, which is the same as calculating the sum total.

Solution:

### Example Question #5 : Arithmetic And Geometric Series

Calculate the sum of the following series:

Explanation:

This is an arithmetic series.

Its general form is

To calculate the sum of very large series such as these, use the formula

This works because you are taking the average of the largest and smallest terms, and then multiplying them by n, which is the same as calculating the sum total.

When k is not equal to 1, split the sums up into 2 piece and take the difference.

Find

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