Answer
$$\frac{-5}{6+\sqrt{5}}=\frac{-30+5\sqrt{5}}{31}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{-5}{6+\sqrt{5}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{-5}{6+\sqrt{5}}\frac{6-\sqrt{5}}{6-\sqrt{5}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{-30+5\sqrt{5}}{36-6\sqrt{5}+6\sqrt{5}-5} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{-30+5\sqrt{5}}{31}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ 6- \sqrt{5}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ -5 } \cdot \left( 6- \sqrt{5}\right) = \color{blue}{-5} \cdot6\color{blue}{-5} \cdot- \sqrt{5} = \\ = -30 + 5 \sqrt{5} $$ Simplify denominator. $$ \color{blue}{ \left( 6 + \sqrt{5}\right) } \cdot \left( 6- \sqrt{5}\right) = \color{blue}{6} \cdot6+\color{blue}{6} \cdot- \sqrt{5}+\color{blue}{ \sqrt{5}} \cdot6+\color{blue}{ \sqrt{5}} \cdot- \sqrt{5} = \\ = 36- 6 \sqrt{5} + 6 \sqrt{5}-5 $$ |
| ③ | Simplify numerator and denominator |
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