Answer
$|a+3|$
Work Step by Step
$\bf{\text{Solution Outline:}}$
Use the properties of radicals to simplify the given expression, $
\sqrt{(a+3)^2}
.$
$\bf{\text{Solution Details:}}$
Since $\sqrt{x^2}=|x|$ for any real value $x,$ the expression above simplifies to
\begin{array}{l}\require{cancel}
\sqrt{(a+3)^2}
\\\\=
|a+3|
.\end{array}