ĐKXĐ: x>=0
\(A=\dfrac{\sqrt{x}\left(x\sqrt{x}-1\right)}{\left(\sqrt{x}+1\right)\left(x+\sqrt{x}+1\right)}-\dfrac{x-3}{\sqrt{x}+1}\)
\(=\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{\sqrt{x}+1}-\dfrac{x-3}{\sqrt{x}+1}\)
\(=\dfrac{x-\sqrt{x}-x+3}{\sqrt{x}+1}=\dfrac{-\sqrt{x}+3}{\sqrt{x}+1}\)
\(=\dfrac{-\sqrt{x}-1+4}{\sqrt{x}+1}=-1+\dfrac{4}{\sqrt{x}+1}\)
\(\dfrac{4}{\sqrt{x}+1}< =\dfrac{4}{1}=4\)
=>\(\dfrac{4}{\sqrt{x}+1}-1< =4-1=3\)
Dấu = xảy ra khi x=0
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