a)\(P=\frac{x-1}{\sqrt{x}\left(\sqrt{x}-1\right)}.\frac{\sqrt{x}-3}{x-1}\)
\(P=\frac{\sqrt{x}-3}{x-\sqrt{x}}\)
b)\(x=\left(\sqrt{2}+1\right)^2\)
\(P=\frac{\sqrt{2}-2}{3+2\sqrt{2}-\sqrt{2}-1}\)\(=-3+2\sqrt{2}\)
c)\(\frac{\sqrt{x}-3}{x-\sqrt{x}}< 0\)
\(\Leftrightarrow x-2\sqrt{x}+3=\left(\sqrt{x}-1\right)^2+2>0\left(LĐ\right)\)