# Chapter 1 - Speaking Mathematically - Exercise Set 1.1: 12

a. real number; product with every number leaves the number unchanged b. with every number leaves the number unchanged c. the product of $r$ and $s$ is $s$ (i.e., $r\times s=s$)

#### Work Step by Step

The real number $r$ is, of course, one, also called the multiplicative identity.

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