Answer
$$\frac{5-\sqrt{18}}{1-\sqrt{2}}=1-2\sqrt{2}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{5-\sqrt{18}}{1-\sqrt{2}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{5-\sqrt{18}}{1-\sqrt{2}}\frac{1+\sqrt{2}}{1+\sqrt{2}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{5+5\sqrt{2}-3\sqrt{2}-6}{1+\sqrt{2}-\sqrt{2}-2} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{-1+2\sqrt{2}}{-1} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}\frac{1-2\sqrt{2}}{1} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle5}{\textcircled {5}} } }}}1-2\sqrt{2}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ 1 + \sqrt{2}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ \left( 5- \sqrt{18}\right) } \cdot \left( 1 + \sqrt{2}\right) = \color{blue}{5} \cdot1+\color{blue}{5} \cdot \sqrt{2}\color{blue}{- \sqrt{18}} \cdot1\color{blue}{- \sqrt{18}} \cdot \sqrt{2} = \\ = 5 + 5 \sqrt{2}- 3 \sqrt{2}-6 $$ Simplify denominator. $$ \color{blue}{ \left( 1- \sqrt{2}\right) } \cdot \left( 1 + \sqrt{2}\right) = \color{blue}{1} \cdot1+\color{blue}{1} \cdot \sqrt{2}\color{blue}{- \sqrt{2}} \cdot1\color{blue}{- \sqrt{2}} \cdot \sqrt{2} = \\ = 1 + \sqrt{2}- \sqrt{2}-2 $$ |
| ③ | Simplify numerator and denominator |
| ④ | Multiply both numerator and denominator by -1. |
| ⑤ | Remove 1 from denominator. |
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