Answer
$0$
Work Step by Step
Substitute $1,2,3,4$ to $k$ and calculate the sum:
$\displaystyle\Sigma_{k=1}^4 \cos k\pi=\cos(\pi)+\cos(2\pi)+\cos(3\pi)+\cos(4\pi)$
$=-1+1-1+1=0$
Thomas' Calculus 13th Edition
by Thomas Jr., George B.
Published by
Pearson
ISBN 10:
0-32187-896-5
ISBN 13:
978-0-32187-896-0
Chapter 5: Integrals - Section 5.2 - Sigma Notation and Limits of Finite Sums - Exercises 5.2 - Page 265: 3
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