Answer
$$\frac{1}{\sqrt{11}-4}=-\frac{\sqrt{11}+4}{5}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{1}{\sqrt{11}-4}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{1}{\sqrt{11}-4}\frac{\sqrt{11}+4}{\sqrt{11}+4} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{\sqrt{11}+4}{11+4\sqrt{11}-4\sqrt{11}-16} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{\sqrt{11}+4}{-5} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}-\frac{\sqrt{11}+4}{5}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ \sqrt{11} + 4} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ 1 } \cdot \left( \sqrt{11} + 4\right) = \color{blue}{1} \cdot \sqrt{11}+\color{blue}{1} \cdot4 = \\ = \sqrt{11} + 4 $$ Simplify denominator. $$ \color{blue}{ \left( \sqrt{11}-4\right) } \cdot \left( \sqrt{11} + 4\right) = \color{blue}{ \sqrt{11}} \cdot \sqrt{11}+\color{blue}{ \sqrt{11}} \cdot4\color{blue}{-4} \cdot \sqrt{11}\color{blue}{-4} \cdot4 = \\ = 11 + 4 \sqrt{11}- 4 \sqrt{11}-16 $$ |
| ③ | Simplify numerator and denominator |
| ④ | Place a negative sign in front of a fraction. |
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