Question
Answer
$$\dfrac{4}{\sqrt{3}+3\sqrt{5}}=\dfrac{-4\sqrt{3}+12\sqrt{5}}{42}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{4}{\sqrt{3}+3\sqrt{5}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{4}{\sqrt{3}+3\sqrt{5}}\frac{\sqrt{3}-3\sqrt{5}}{\sqrt{3}-3\sqrt{5}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{4\sqrt{3}-12\sqrt{5}}{3-3\sqrt{15}+3\sqrt{15}-45} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{4\sqrt{3}-12\sqrt{5}}{-42} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}\frac{-4\sqrt{3}+12\sqrt{5}}{42}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ \sqrt{3}- 3 \sqrt{5}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ 4 } \cdot \left( \sqrt{3}- 3 \sqrt{5}\right) = \color{blue}{4} \cdot \sqrt{3}+\color{blue}{4} \cdot- 3 \sqrt{5} = \\ = 4 \sqrt{3}- 12 \sqrt{5} $$ Simplify denominator. $$ \color{blue}{ \left( \sqrt{3} + 3 \sqrt{5}\right) } \cdot \left( \sqrt{3}- 3 \sqrt{5}\right) = \color{blue}{ \sqrt{3}} \cdot \sqrt{3}+\color{blue}{ \sqrt{3}} \cdot- 3 \sqrt{5}+\color{blue}{ 3 \sqrt{5}} \cdot \sqrt{3}+\color{blue}{ 3 \sqrt{5}} \cdot- 3 \sqrt{5} = \\ = 3- 3 \sqrt{15} + 3 \sqrt{15}-45 $$ |
| ③ | Simplify numerator and denominator |
| ④ | Multiply both numerator and denominator by -1. |
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