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

True, $f=g$

This is true. The variables x and u represent the domain 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