Question

Rút gọn : \(\frac{7\sqrt{b}}{b-9}-\left(\frac{\sqrt{b}}{\sqrt{b}-3}-\frac{\sqrt{b}-1}{\sqrt{b}+3}\right)\)

Answer 1

\(\frac{7\sqrt{b}}{b-9}-\left(\frac{\sqrt{b}}{\sqrt{b}-3}-\frac{\sqrt{b}-1}{\sqrt{b}+3}\right)\)

\(=\frac{7\sqrt{b}}{b-9}-\frac{\sqrt{b}\times\left(\sqrt{b}+3\right)}{\left(\sqrt{b}-3\right)\left(\sqrt{b}+3\right)}+\frac{\left(\sqrt{b}-1\right)\left(\sqrt{b}-3\right)}{\left(\sqrt{b}+3\right)\left(\sqrt{b}-3\right)}\)

\(=\frac{7\sqrt{b}}{b-9}-\frac{b+3\sqrt{b}}{b-9}+\frac{b-3\sqrt{b}-\sqrt{b}+3}{b-9}\)

\(=\frac{7\sqrt{b}-b-3\sqrt{b}+b-3\sqrt{b}-\sqrt{b}+3}{b-9}\)

\(=\frac{3}{b-9}\)