a, đk x >= 0 ; x khác 1
\(P=\left(\dfrac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)-\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}{\left(x-1\right)\left(\sqrt{x}+1\right)}\right):\left(-\dfrac{2}{\left(x-1\right)^2}\right)\)
\(=\left(\dfrac{x-\sqrt{x}-2-x-\sqrt{x}+2}{\left(x-1\right)\left(\sqrt{x}+1\right)}\right):\left(-\dfrac{2}{\left(x-1\right)^2}\right)=\dfrac{2\sqrt{x}\left(x-1\right)^2}{\left(x-1\right)\left(\sqrt{x}+1\right)2}=\dfrac{\sqrt{x}\left(x-1\right)}{\sqrt{x}+1}\)
b, Ta có \(\sqrt{x}=\sqrt{\left(2-\sqrt{3}\right)^2}=2-\sqrt{3}\)
\(P=\dfrac{\left(2-\sqrt{3}\right)\left(6-4\sqrt{3}\right)}{3-\sqrt{3}}=\dfrac{\left(2-\sqrt{3}\right)\left(6-4\sqrt{x}\right)\left(3+\sqrt{3}\right)}{6}\)
