a: \(=\dfrac{x+5\sqrt{x}-10\sqrt{x}-5\sqrt{x}+25}{x-25}=\dfrac{x-10\sqrt{x}+25}{x-25}\)
\(=\dfrac{\sqrt{x}-5}{\sqrt{x}+5}\)
b: Khi x=9 thì \(A=\dfrac{3-5}{3+5}=\dfrac{-2}{8}=\dfrac{-1}{4}\)
c: Để A=1/2 thì \(\dfrac{\sqrt{x}-5}{\sqrt{x}+5}=\dfrac{1}{2}\)
=>\(2\sqrt{x}-10=\sqrt{x}+5\)
=>x=225
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