<|system|>
Rationalize the denominator of $\displaystyle\frac{21}{\sqrt{21}}$.</s>.
<|user|>
Can you answer based on context?
<|assistant|>
$\dfrac{21}{\sqrt{21}} = \dfrac{21}{\sqrt{21}} \cdot \dfrac{\sqrt{21}}{\sqrt{21}} = \dfrac{21\sqrt{21}}{21} = \!\sqrt{21}$.