c) Chứng minh B = căn x /(căn x − 2) .

c) Với \(x > 0,\,\,x \ne 4\), ta có

B=x−1x+2+5x−2x−4=x−1x−2x+2x−2+5x−2x+2x−2

\( = \frac{{x - 3\sqrt x + 2 + 5\sqrt x - 2}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}} = \frac{{x + 2\sqrt x }}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}}\)

\( = \frac{{\sqrt x \left( {\sqrt x + 2} \right)}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}} = \frac{{\sqrt x }}{{\sqrt x - 2}}\).