$\displaystyle \begin{array}{{>{\displaystyle}l}}
a)\sqrt{x}\left(\sqrt{x} +3\right) +2\sqrt{x}\left(\sqrt{x} -3\right) -( 3x-9) =0\ \\
x+3\sqrt{x} +2x-6\sqrt{x} -3x+9=0\ \\
3\sqrt{x} =9\ \\
DK:\ x\geqslant 0\ \\
\rightarrow \sqrt{x} =3\ \\
\rightarrow x=9\ ( tm) \ \\
Vậy....\ \\
b) \ 2\sqrt{x}\left(\sqrt{x} +2\right) -2\sqrt{x}\left(\sqrt{x} -4\right) -\left( 4\sqrt{x} +16\right) =0\\
2x+4\sqrt{x} -2x+8\sqrt{x} -4\sqrt{x} -16=0\ \\
DK\ :x\geqslant 0\ \\
8\sqrt{x} =16\ \\
\rightarrow \sqrt{x} =2\ \\
\rightarrow x=4\ ( tm) \ \\
Vậy.......\ \\
c) \ \left(\sqrt{x} +1\right)^{2} -\sqrt{x}\left(\sqrt{x} -2\right) +\sqrt{x} -9=0\ \\
DK\ :x\geqslant 0\ \\
x+2\sqrt{x} +1-x+2\sqrt{x} +\sqrt{x} -9=0\ \\
5\sqrt{x} =8\ \\
\rightarrow \sqrt{x} =\frac{8}{5} \ \\
\rightarrow x=\frac{64}{25} \ ( tmdk) \ \\
Vậy..........\
\end{array}$
