Question
Answer
$$\dfrac{7}{2\sqrt{5}-4}=\dfrac{14\sqrt{5}+28}{4}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{7}{2\sqrt{5}-4}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{7}{2\sqrt{5}-4}\frac{2\sqrt{5}+4}{2\sqrt{5}+4} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{14\sqrt{5}+28}{20+8\sqrt{5}-8\sqrt{5}-16} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{14\sqrt{5}+28}{4}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ 2 \sqrt{5} + 4} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ 7 } \cdot \left( 2 \sqrt{5} + 4\right) = \color{blue}{7} \cdot 2 \sqrt{5}+\color{blue}{7} \cdot4 = \\ = 14 \sqrt{5} + 28 $$ Simplify denominator. $$ \color{blue}{ \left( 2 \sqrt{5}-4\right) } \cdot \left( 2 \sqrt{5} + 4\right) = \color{blue}{ 2 \sqrt{5}} \cdot 2 \sqrt{5}+\color{blue}{ 2 \sqrt{5}} \cdot4\color{blue}{-4} \cdot 2 \sqrt{5}\color{blue}{-4} \cdot4 = \\ = 20 + 8 \sqrt{5}- 8 \sqrt{5}-16 $$ |
| ③ | Simplify numerator and denominator |
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