a; ĐKXĐ: x>=0; x<>1
\(P=\dfrac{x+\sqrt{x}-6\sqrt{x}+4+3\sqrt{x}-3}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{x-2\sqrt{x}+1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}=\dfrac{\sqrt{x}-1}{\sqrt{x}+1}\)
b: Thay \(x=3-\sqrt{8}\) vào P, ta được:
\(P=\dfrac{\sqrt{2}-1-1}{\sqrt{2}-1+1}=\dfrac{\sqrt{2}-2}{\sqrt{2}}=1-\sqrt{2}\)