9:A>0
=>căn x-1>0
=>x>1
\(B-3=\dfrac{x-\sqrt{x}+1-\sqrt{x}+1}{\sqrt{x}-1}=\dfrac{x+2}{\sqrt{x}-1}\)
\(=\dfrac{x-1+3}{\sqrt{x}-1}\)
\(=\sqrt{x}+1+\dfrac{3}{\sqrt{x}-1}\)
\(=\sqrt{x}-1+\dfrac{3}{\sqrt{x}-1}+2>=2\sqrt{3}+2>0\)
=>B>3
7:
\(A=\dfrac{\left(\sqrt{x}-3\right)^2}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\dfrac{\sqrt{x}-3}{\sqrt{x}+3}\)
|A|=-A
=>A<=0
=>căn x-3<=0
=>0<=x<9
mà x lớn nhất
nên x=8
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