Chapter 10 - Section 10.1 - Radical Expressions and Radical Functions - Practice - Page 683: 29

$x+3$

Using the rule given in the book: If $n$ is an even positive integer, then $\sqrt[n]{a^n} = |a|$ If $n$ is an odd positive integer, then $\sqrt[n]{a^n} = a$ We get $\sqrt{x^2+6x+9} = \sqrt{(x+3)^2} \rightarrow |x+3| = x+3$