Answer
$$\frac{13}{\sqrt{21}}=\frac{13\sqrt{21}}{21}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{13}{\sqrt{21}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}} \frac{ 13 }{\sqrt{ 21 }} \times \frac{ \color{orangered}{\sqrt{ 21 }} }{ \color{orangered}{\sqrt{ 21 }}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{13\sqrt{21}}{21}\end{aligned} $$ | |
| ① | Multiply both top and bottom by $ \color{orangered}{ \sqrt{ 21 }}$. |
| ② | In denominator we have $ \sqrt{ 21 } \cdot \sqrt{ 21 } = 21 $. |
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