ĐKXĐ: \(x\ge 0;x\ne \dfrac{1}{9}\)
\(B=(1-\dfrac{2\sqrt x}{3\sqrt x+1}+\dfrac{\sqrt x+1}{9x-1}):(\dfrac{9\sqrt x+6}{3\sqrt x+1}-3)\\=(\dfrac{(3\sqrt x-1)(3\sqrt x+1)}{(3\sqrt x-1)(3\sqrt x+1)}-\dfrac{2\sqrt x(3\sqrt x-1)}{(3\sqrt x+1)(3\sqrt x-1)}+\dfrac{\sqrt x+1}{(3\sqrt x+1)(3\sqrt x-1)}):(\dfrac{9\sqrt x+6}{3\sqrt x+1}-\dfrac{3(3\sqrt x+1)}{3\sqrt x+1})\\=\dfrac{9x-1-6x+2\sqrt x+\sqrt x+1}{(3\sqrt x+1)(3\sqrt x-1)}:\dfrac{9\sqrt x+6-9\sqrt x-3}{3\sqrt x+1}\\=\dfrac{3x+3\sqrt x}{(3\sqrt x-1)(3\sqrt x+1)}.\dfrac{3\sqrt x+1}{3}\\=\dfrac{3(x+\sqrt x)(3\sqrt x+1)}{(3\sqrt x-1)(3\sqrt x+1).3}\\=\dfrac{x+\sqrt x}{3\sqrt x-1}\)
