a: ĐKXĐ: x>0; x<>1
b: \(P=\left(\dfrac{\sqrt{x}+1}{x+\sqrt{x}+1}-\dfrac{1}{\sqrt{x}+1}\right):\dfrac{x+1-2\sqrt{x}}{\left(\sqrt{x}-1\right)\left(x+1\right)}\)
\(=\dfrac{x+2\sqrt{x}+1-x-\sqrt{x}-1}{\left(\sqrt{x}+1\right)\left(x+\sqrt{x}+1\right)}\cdot\dfrac{\left(\sqrt{x}-1\right)\left(x+1\right)}{\left(\sqrt{x}-1\right)^2}\)
\(=\dfrac{\sqrt{x}}{\left(\sqrt{x}+1\right)\left(x+\sqrt{x}+1\right)}\cdot\dfrac{x+1}{\sqrt{x}-1}\)