Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 5 - Number Theory and the Real Number System - 5.7 Arithmetic and Geometric Sequences - Exercise Set 5.7 - Page 330: 115

Answer

The sequence is arithmetic and the sum of the first $10$ terms is $310$.

Work Step by Step

The terms have a common difference of $6$ so the sequence is arithmetic with $d=6$ and $a_1=4$. The sum $S_n$ of the first $n$ terms of an arithmetic sequence is given by the formula: $$S_n=\frac{n}{2}(a_1+a_n)$$ The given sequence has $a_1=4$ and $d=6$. However, the value of $a_{10}$ is not yet known. Solve for $a_{10}$ using the formula $a_n=a_1+(n-1)(d)$ to obtain: \begin{align*} a_{10}=4+(10-1)(6)\\ &=4+9(6)\\ &=4+54\\ &=58 \end{align*} Use the formula for the sum of the first $n$ terms to obtain the sum of the first $10$ terms (use $n=10$) to obtain: \begin{align*} S_{10}=\frac{10}{2}(4+58)\\ &=5(62)\\ &=310 \end{align*}
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