Chapter 1 - Functions and Limits - 1.1 Four Ways to Represent a Function - 1.1 Exercises - Page 19: 1

True

This is true. The variables $x$ and $u$ represent the variable of the functions $f$ and $g$ respectively, and we can substitute any values (i.e. values in (-$\infty$,$\infty$)) for either $x$ or $u$ and we will still get the same value for both $f$ and $g$ as the formula for each of the two functions is the same..