Đáp án:
Giải thích các bước giải:
`A=\sqrt{9x^2}-2x`
`A=\sqrt{9}.\sqrt{x^2}-2x`
`A=3|x|-2x`
`A=-3x-2x` (do `x<0)`
`A=-5x`
`B=\frac{\sqrt{a}+\sqrt{b}}{\sqrt{a}-\sqrt{b}}+\frac{\sqrt{a}-\sqrt{b}}{\sqrt{a}+\sqrt{b}}`
ĐK: `a,b \ge 0, a \ne b`
`B=\frac{(\sqrt{a}+\sqrt{b})^2}{(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})}+\frac{(\sqrt{a}-\sqrt{b})^2}{(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})}`
`B=\frac{a+2\sqrt{ab}+b}{(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})}+\frac{a-2\sqrt{ab}+b}{(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})}`
`B=\frac{a+2\sqrt{ab}+b+a-2\sqrt{ab}+b}{(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})}`
`B=\frac{2a+2b}{a-b}`
`B=\frac{2(a+b)}{a-b}`
