Answer
$$\frac{9}{9-\sqrt{7}}=\frac{81+9\sqrt{7}}{74}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{9}{9-\sqrt{7}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{9}{9-\sqrt{7}}\frac{9+\sqrt{7}}{9+\sqrt{7}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{81+9\sqrt{7}}{81+9\sqrt{7}-9\sqrt{7}-7} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{81+9\sqrt{7}}{74}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ 9 + \sqrt{7}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ 9 } \cdot \left( 9 + \sqrt{7}\right) = \color{blue}{9} \cdot9+\color{blue}{9} \cdot \sqrt{7} = \\ = 81 + 9 \sqrt{7} $$ Simplify denominator. $$ \color{blue}{ \left( 9- \sqrt{7}\right) } \cdot \left( 9 + \sqrt{7}\right) = \color{blue}{9} \cdot9+\color{blue}{9} \cdot \sqrt{7}\color{blue}{- \sqrt{7}} \cdot9\color{blue}{- \sqrt{7}} \cdot \sqrt{7} = \\ = 81 + 9 \sqrt{7}- 9 \sqrt{7}-7 $$ |
| ③ | Simplify numerator and denominator |
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