\(B=\left(\dfrac{\sqrt{x}+2}{\sqrt{x}-1}-\dfrac{\sqrt{x}+1}{\sqrt{x}-3}+\dfrac{3\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}\right):\left(1-\dfrac{1}{\sqrt{x}-1}\right)=\dfrac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-3\right)-\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)+3\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}:\dfrac{\sqrt{x}-1-1}{\sqrt{x}-1}=\dfrac{x-\sqrt{x}-6-x+1+3\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}.\)
\(\dfrac{\sqrt{x}-1}{\sqrt{x}-2}=\dfrac{2\sqrt{x}-6}{\left(\sqrt{x}-1\right)\left(\sqrt{x}-3\right)}.\dfrac{\sqrt{x}-1}{\sqrt{x}-2}=\dfrac{2\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}=\dfrac{2}{\sqrt{x}-2}\)
Để B=3 thì \(\dfrac{2}{\sqrt{x}-2}=3\left(ĐKXĐ:x\ge0.và.x\ne4\right)\)
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