$ĐKXĐ: x\ge0; x\ne25$
$B=(\dfrac{15-\sqrt{x}}{x-25}+\dfrac{2}{\sqrt{x}+5}):\dfrac{\sqrt{x}+1}{\sqrt{x}-5}$
$B=(\dfrac{15-\sqrt{x}}{(\sqrt{x}+5)(\sqrt{x}-5)}+\dfrac{2}{\sqrt{x}+5}).\dfrac{\sqrt{x}-5}{\sqrt{x}+1}$
$B=\dfrac{(15-\sqrt{x})+2(\sqrt{x}-5)}{(\sqrt{x}+5)(\sqrt{x}-5)}.\dfrac{\sqrt{x}-5}{\sqrt{x}+1}$
$B=\dfrac{15-\sqrt{x}+2\sqrt{x}-10}{(\sqrt{x}+5)(\sqrt{x}-5)}.\dfrac{\sqrt{x}-5}{\sqrt{x}+1}$
$B=\dfrac{\sqrt{x}+5}{(\sqrt{x}+5)(\sqrt{x}-5)}.\dfrac{\sqrt{x}-5}{\sqrt{x}+1}$
$B=\dfrac{1}{\sqrt{x}+1}$
Vậy với $x\ge0; x\ne5$ thì $B=\dfrac{1}{\sqrt{x}+1}$
