Question

Answer 1

a: Khi x=25/4 thì \(A=\left(\dfrac{5}{2}-5\right):\left(\dfrac{5}{2}+5\right)=\dfrac{-5}{2}:\dfrac{15}{2}=\dfrac{-1}{3}\)

b: Để A=1/3 thì \(\dfrac{\sqrt{x}-5}{\sqrt{x}+5}=\dfrac{1}{3}\)

\(\Leftrightarrow3\sqrt{x}-15=\sqrt{x}+5\)

=>\(2\sqrt{x}=20\)

=>x=100

c: Để \(A=\dfrac{-2}{3}\sqrt{x}\) thì \(\sqrt{x}=\dfrac{\sqrt{x}-5}{\sqrt{x}+5}:\dfrac{-2}{3}=\dfrac{3\sqrt{x}-15}{-2\sqrt{x}-10}\)

\(\Leftrightarrow-2x-10\sqrt{x}=3\sqrt{x}-15\)

\(\Leftrightarrow2x+10\sqrt{x}=-3\sqrt{x}+15\)

\(\Leftrightarrow2x+13\sqrt{x}-15=0\)

\(\Leftrightarrow\left(2\sqrt{x}+15\right)\left(\sqrt{x}-1\right)=0\)

=>x=1(nhận)