Question

Rút gọn biểu thức B= \(\left(\dfrac{1}{\sqrt{x}+3}+\dfrac{1}{\sqrt{x}-3}\right)\left(1-\dfrac{3}{\sqrt{x}}\right)\)

Answer 1

\(B=\left(\dfrac{1}{\sqrt{x}+3}+\dfrac{1}{\sqrt{x}-3}\right)\left(1-\dfrac{3}{\sqrt{x}}\right)\)

\(=\left(\dfrac{\sqrt{x}-3+\sqrt{x}+3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\right)\left(\dfrac{\sqrt{x}-3}{\sqrt{x}}\right)\)

\(=\dfrac{2\sqrt{x}}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}.\dfrac{\sqrt{x}-3}{\sqrt{x}}\)

\(=\dfrac{2}{\sqrt{x}+3}\)

Vậy \(B=\dfrac{2}{\sqrt{x}+3}\)