Chapter 10 - Radical Expressions and Equations - 10-5 Graphing Square Root Functions - Practice and Problem-Solving Exercises - Page 629: 13

$ x \leq 18 $

You can not take the square root of a negative number. Therefore, $18 - x$ must be greater than or equal to 0. $ 18 - x \geq 0$ We subtract 18 from both sides $ - x \geq -18 $ We divide both sides by -1. *** When we multiply by a negative number we flip the inequality sign. $ x \leq 18 $