[tex]\bf \sqrt{2x+30}=x+3\impliedby \textit{we'll squares both sides}
\\\\\\
(\sqrt{2x+30})^2=(x+3)^2\implies 2x+30=x^2+6x+9
\\\\\\
0=x^2+4x-21\implies 0=(x+7)(x-3)\implies x=
\begin{cases}
-7\\
3
\end{cases}[/tex]
I don't see an extraneous value there, -7 checks out well if you plug it in the original equation, and so does 3.