Answer
$2x-2\sqrt[]{2x+5}+6$
Work Step by Step
Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, then,
\begin{array}{l}
\left( \sqrt[]{2x+5}-1 \right)^2
\\=
(\sqrt[]{2x+5})^2+2(\sqrt[]{2x+5})(-1)+(-1)^2
\\=
2x+5-2\sqrt[]{2x+5}+1
\\=
2x-2\sqrt[]{2x+5}+6
.\end{array}