$\displaystyle \begin{array}{{>{\displaystyle}l}} B=\frac{4}{\sqrt{x} +1} -\frac{2}{\sqrt{x} -1} -\frac{\sqrt{x} -5}{x-1} \ ĐK:\ x\geqslant 0,\ x\neq 1\\ B=\frac{4\sqrt{x} -4-2\sqrt{x} -2-\sqrt{x} +5}{\left(\sqrt{x} -1\right)\left(\sqrt{x} +1\right)}\\ B=\frac{\sqrt{x} -1}{\left(\sqrt{x} -1\right)\left(\sqrt{x} +1\right)} =\frac{1}{\sqrt{x} +1}\\ \frac{A}{B} =\frac{\sqrt{x} -5}{\sqrt{x} +1} .\left(\sqrt{x} +1\right) =\sqrt{x} -5=\frac{1}{4}\\ \Leftrightarrow \sqrt{x} =\frac{21}{4} \ \\ \Leftrightarrow x=\frac{441}{16} \ ( TM) \end{array}$
