Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 11 - Further Topics in Algebra - 11.2 Arithmetic Sequences and Series - 11.2 Exercises - Page 1024: 9

Answer

$$\sum\limits_{i = 1}^5 {\left( {4i - 1} \right)} = 55$$

Work Step by Step

$$\eqalign{ & \sum\limits_{i = 1}^5 {\left( {4i - 1} \right)} \cr & {\text{The first term is}} \cr & {a_1} = 4\left( 1 \right) - 1 = 3 \cr & {\text{The last term is}} \cr & {a_5} = 4\left( 5 \right) - 1 = 19 \cr & {\text{Using the formula }}{S_n} = \frac{n}{2}\left( {{a_1} + {a_n}} \right),{\text{ we obtain}} \cr & \sum\limits_{i = 1}^5 {\left( {4i - 1} \right)} = {S_5} = \frac{5}{2}\left( {3 + 19} \right) \cr & \sum\limits_{i = 1}^5 {\left( {4i - 1} \right)} = 55 \cr} $$
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