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 1025: 55



Work Step by Step

We are looking for the sum of the first 80 positive integers. Use the formula $S_n=\frac{n}{2}(a_1+a_n)$ with $n=80, a_1=1, a_{80}=80$: $S_n=\frac{n}{2}(a_1+a_n)$ $S_{80}=\frac{80}{2}(1+80)$ $S_{80}=40*81$ $S_{80}=\boxed{3240}$
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