Câu 19:
a: \(P=\left(\dfrac{2\sqrt{x}}{\sqrt{x}+3}+\dfrac{\sqrt{x}}{\sqrt{x}-3}-\dfrac{3x+3}{x-9}\right):\dfrac{2\sqrt{x}-2-\sqrt{x}+3}{\sqrt{x}-3}\)
\(=\dfrac{2x-6\sqrt{x}+x+3\sqrt{x}-3x-3}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\cdot\dfrac{\sqrt{x}-3}{\sqrt{x}+1}\)
\(=\dfrac{-3\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\cdot\dfrac{1}{\sqrt{x}+3}=\dfrac{-3}{\sqrt{x}+3}\)
b: Để P<-1/3 thì P+1/3<0
\(\Leftrightarrow-\dfrac{3}{\sqrt{x}+3}+\dfrac{1}{3}< 0\)
\(\Leftrightarrow-9+\sqrt{x}+3< 0\)
hay 0<x<36
Kết hợp ĐKXĐ, ta được: \(\left\{{}\begin{matrix}0< x< 36\\x< >9\end{matrix}\right.\)
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