Rút gọn : \(\frac{\sqrt{x}}{\sqrt{x}+5}+\frac{10\sqrt{x}}{25-x}-\frac{5}{\sqrt{x}+5}\)
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\(\frac{x+\sqrt{5}}{x^2+2\sqrt{5}x+5}=\frac{x+\sqrt{5}}{\left(x+\sqrt{5}\right)^2}=\frac{1}{x+\sqrt{5}}\)
\(B=\frac{x+\sqrt{5}}{x^2+2\sqrt{5}x+5}=\frac{x+\sqrt{5}}{\left(x+\sqrt{5}\right)^2}=\frac{1}{x+\sqrt{5}}=\frac{x-\sqrt{5}}{x^2-5}\)
A=căn[(x-5)2]/x-5=|x-5|/x-5
Nếu x>=5 thì A=1
Nếu x<5 thì A=-1
Sửa đề; \(D=\left(\dfrac{\sqrt{x}+\sqrt{y}}{2\sqrt{x}-2\sqrt{y}}-\dfrac{2\sqrt{xy}}{x-y}\right)\cdot\dfrac{2\sqrt{x}}{\sqrt{x}-\sqrt{y}}\)
\(D=\dfrac{x+2\sqrt{xy}+y-4\sqrt{xy}}{2\left(x-y\right)}\cdot\dfrac{2\sqrt{x}}{\sqrt{x}-\sqrt{y}}\)
\(=\dfrac{\left(\sqrt{x}-\sqrt{y}\right)^2}{\sqrt{x}-\sqrt{y}}\cdot\dfrac{\sqrt{x}}{x-y}=\dfrac{\sqrt{x}}{\sqrt{x}+\sqrt{y}}\)
\(\left(\frac{\sqrt{x}}{\sqrt{x}-1}-\frac{1}{x-\sqrt{x}}\right):\left(\frac{1}{x+\sqrt{x}}-\frac{2}{1-x}\right)\) (ĐKXĐ : \(x>0;x\ne1;x\ne\frac{1}{9}\) )
\(=\left[\frac{x}{\sqrt{x}\left(\sqrt{x}-1\right)}-\frac{1}{\sqrt{x}\left(\sqrt{x}-1\right)}\right]:\left[\frac{\sqrt{x}-1}{\sqrt{x}.\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}+\frac{2\sqrt{x}}{\sqrt{x}.\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\right]\)
\(=\frac{\sqrt{x}+1}{\sqrt{x}}:\frac{3\sqrt{x}-1}{\sqrt{x}\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\frac{\sqrt{x}+1}{\sqrt{x}}.\frac{\sqrt{x}\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{3\sqrt{x}-1}\)
\(=\frac{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}{3\sqrt{x}-1}\)
\(=\dfrac{x-10\sqrt{x}+25-10\sqrt{x}}{x-25}=\dfrac{x-20\sqrt{x}+25}{x-25}\)