## Precalculus (6th Edition) Blitzer

Published by Pearson

# Chapter 10 - Section 10.1 - Sequences and Summation Notation - Concept and Vocabulary Check - Page 1048: 6

#### Answer

$5!$ is called "5 factorial" and is the product of all positive integers from 5 down through 1. By definition, $0!$ = 1.

#### Work Step by Step

Taking n as a positive integer, the notation $n!$ (read "n factorial”) is defined as the product of all positive integers from n down through 1. We can write this as $n!=n(n-1)(n-2)(n-3).......(3)(2)(1)$. Now for $n=5$, $5!=5\times 4\times 3\times 2\times 1$ And, \begin{align} & n!=n(n-1)! \\ & 1!=1(0)! \\ & 0!=1 \end{align}

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