$$B= \frac{ x+5 }{ 2x+1 } \times \frac{ 2x+1 }{ x+5 }$$
$B=1$
$x\neq -\frac{1}{2}\text{ and }x\neq -5$
$x\in \mathrm{C}\setminus -\frac{1}{2},-5$
$B=1\text{ and }x\neq -\frac{1}{2}\text{ and }x\neq -5$
$x\in \mathrm{R}\setminus -\frac{1}{2},-5$
$B=1\text{ and }x\neq -\frac{1}{2}\text{ and }x\neq -5$
