`***`Lời giải`***`
66)
ĐKXĐ: `x>0;xne1`
`A=(\frac{1}{x+\sqrt{x}}-\frac{1}{\sqrt{x}+1}):\frac{\sqrt{x}-1}{x+2\sqrt{x}+1}+1`
`=(\frac{1}{\sqrt{x}(\sqrt{x}+1)}-\frac{1}{\sqrt{x}+1}):\frac{\sqrt{x}-1}{x+2\sqrt{x}+1}+1`
`=\frac{1-\sqrt{x}}{\sqrt{x}(\sqrt{x}+1)}:\frac{\sqrt{x}-1}{x+2\sqrt{x}+1}+1`
`=-\frac{\sqrt{x}-1}{\sqrt{x}(\sqrt{x}+1)}:\frac{\sqrt{x}-1}{(\sqrt{x}+1)^2}+1`
`=-\frac{\sqrt{x}-1}{\sqrt{x}(\sqrt{x}+1)}.\frac{(\sqrt{x}+1)^2}{ \sqrt{x}-1 }+1`
`=\frac{-(\sqrt{x}+1)}{ \sqrt{x}}+1`
`=\frac{-(\sqrt{x}+1)+\sqrt{x}}{ \sqrt{x}}`
`=\frac{-\sqrt{x}-1+\sqrt{x}}{ \sqrt{x}}`
`=\frac{-1}{ \sqrt{x}}`
