University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 5 - Section 5.2 - Sigma Notation and Limits of Finite Sums - Exercises - Page 299: 6



Work Step by Step

$\sum\limits_{k=1}^4(-1)^{k}cos {(k\cdot\pi)}=(-1)^{1}cos( {1\cdot\pi})+(-1)^{2}cos( {2\cdot\pi})+(-1)^{3}cos( {3\cdot\pi})+(-1)^{4}cos ({4\cdot\pi})=-cos( {1\cdot\pi})+cos( {2\cdot\pi})+-cos( {3\cdot\pi})+cos ({4\cdot\pi})=1+1+1+1=4$
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