Chapter 11: Q 112. (page 1069)

In the following exercises, find the sum of the first 30 terms of each arithmetic sequence.
−15, −12, −9, −6, −3, …

Short Answer

Expert verified

The obtained value is 855.

Step by step solution

Step 1. Given Information.

The arithmetic sequence is −15, −12, −9, −6, −3, ….

Step 2. Find the common difference d.

Find the common difference of consecutive terms.

$\begin{array}{rcl} d & = & - 12 - (- 15) \\ = & 3 \end{array}$

And, now find the 30^th term of the sequence.

$\begin{array}{rcl} a_{30} & = & - 15 + (30 - 1) 3 \\ = & - 15 + 87 \\ = & 72 \end{array}$

Step 3. Use the sum formula.

Use the sum formula $S_{n} = \frac{n}{2} (a_{1} + a_{n})$ to find the sum of the thirtieth term.

$\begin{array}{rcl} S_{30} & = & \frac{30}{2} (- 15 + 72) \\ = & 15 (57) \\ = & 855 \end{array}$

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In the following exercises, find the sum of the first 30 terms of each arithmetic sequence.
−15, −12, −9, −6, −3, …

Short Answer

Step by step solution

Step 1. Given Information.

Step 2. Find the common difference d.

Step 3. Use the sum formula.

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In the following exercises, find the sum of the first 30 terms of each arithmetic sequence. −15, −12, −9, −6, −3, …

Short Answer

Step by step solution

Step 1. Given Information.

Step 2. Find the common difference d.

Step 3. Use the sum formula.

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Math Textbooks

Pure Maths

Probability and Statistics

Geometry

Mechanics Maths

Discrete Mathematics

Applied Mathematics

Study anywhere. Anytime. Across all devices.

In the following exercises, find the sum of the first 30 terms of each arithmetic sequence.
−15, −12, −9, −6, −3, …