Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 12 - Sequences; Induction; the Binomial Theorem - Chapter Review - Review Exercises - Page 839: 29



Work Step by Step

Note that ${n\choose j}=\frac{n!}{(n-j)!j!}$. Hence, ${5\choose 2}=\dfrac{5!}{(5-2)!2!}=\dfrac{5\cdot4\cdot3\cdot2\cdot1}{3\cdot2\cdot1\cdot2\cdot1}=10$
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