Question
Answer
$$\dfrac{7+6\sqrt{5}}{7-6\sqrt{5}}=-\dfrac{229+84\sqrt{5}}{131}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{7+6\sqrt{5}}{7-6\sqrt{5}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{7+6\sqrt{5}}{7-6\sqrt{5}}\frac{7+6\sqrt{5}}{7+6\sqrt{5}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{49+42\sqrt{5}+42\sqrt{5}+180}{49+42\sqrt{5}-42\sqrt{5}-180} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{229+84\sqrt{5}}{-131} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}-\frac{229+84\sqrt{5}}{131}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ 7 + 6 \sqrt{5}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ \left( 7 + 6 \sqrt{5}\right) } \cdot \left( 7 + 6 \sqrt{5}\right) = \color{blue}{7} \cdot7+\color{blue}{7} \cdot 6 \sqrt{5}+\color{blue}{ 6 \sqrt{5}} \cdot7+\color{blue}{ 6 \sqrt{5}} \cdot 6 \sqrt{5} = \\ = 49 + 42 \sqrt{5} + 42 \sqrt{5} + 180 $$ Simplify denominator. $$ \color{blue}{ \left( 7- 6 \sqrt{5}\right) } \cdot \left( 7 + 6 \sqrt{5}\right) = \color{blue}{7} \cdot7+\color{blue}{7} \cdot 6 \sqrt{5}\color{blue}{- 6 \sqrt{5}} \cdot7\color{blue}{- 6 \sqrt{5}} \cdot 6 \sqrt{5} = \\ = 49 + 42 \sqrt{5}- 42 \sqrt{5}-180 $$ |
| ③ | Simplify numerator and denominator |
| ④ | Place a negative sign in front of a fraction. |
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