Bài 4:
\(\left(\frac{\sqrt{x}}{\sqrt{x}-2}+\frac{\sqrt{x}}{\sqrt{x}+2}\right)\cdot\frac{x-4}{\sqrt{4x}}\)
\(=\frac{\sqrt{x}\left(\sqrt{x}+2\right)+\sqrt{x}\left(\sqrt{x}-2\right)}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\cdot\frac{\left.\left(x-4\right)\right.}{2\sqrt{x}}\)
\(=\frac{x+2\sqrt{x}+x-2\sqrt{x}}{x-4}\cdot\frac{x-4}{2\sqrt{x}}=\frac{2x}{2\sqrt{x}}=\sqrt{x}\)
Bài 3:
a: \(\frac{3}{\sqrt8+\sqrt5}=\frac{3\left(\sqrt8-\sqrt5\right)}{\left(\sqrt8+\sqrt5\right)\left(\sqrt8-\sqrt5\right)}=\frac{3\left(\sqrt8-\sqrt5\right)}{8-5}=\sqrt8-\sqrt5\)
b: \(\frac{2}{\sqrt{a}-\sqrt{b}}=\frac{2\left(\sqrt{a}+\sqrt{b}\right)}{\left(\sqrt{a}-\sqrt{b}\right)\left(\sqrt{a}+\sqrt{b}\right)}=\frac{2\left(\sqrt{a}+\sqrt{b}\right)}{a-b}\)
c: \(\frac{x}{\sqrt{x}+5}=\frac{x\left(\sqrt{x}-5\right)}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}=\frac{x\left(\sqrt{x}-5\right)}{x-25}\)
