Toán 9 Toán 9 ôn c3

7 1 2 5

7 1 2 5

Cựu TMod Toán
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19 Tháng một 2019
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a) [tex]A=\frac{15\sqrt{x}-11}{x+2\sqrt{x}-3}+\frac{3\sqrt{x}-2}{1-\sqrt{x}}-\frac{2\sqrt{x}+3}{\sqrt{x}+3}=\frac{15\sqrt{x}-11-(3\sqrt{x}-2)(\sqrt{x}+3)-(2\sqrt{x}+3)(\sqrt{x}-1)}{(\sqrt{x}-1)(\sqrt{x}+3)}=\frac{-5x+7\sqrt{x}-2}{(\sqrt{x}-1)(\sqrt{x}+3)}=\frac{(\sqrt{x}-1)(-5\sqrt{x}+2)}{(\sqrt{x}-1)(\sqrt{x}+3)}=\frac{-5\sqrt{x}+2}{\sqrt{x}+3}[/tex]
b)[tex]A+5=\frac{-5\sqrt{x}+2}{\sqrt{x}+3}+5=\frac{17}{\sqrt{x}+3}\leq \frac{17}{3}\Rightarrow A\leq \frac{2}{3}[/tex]
 
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