Evaluate
\frac{\sqrt{21}}{6}\approx 0.763762616
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\frac{42\sqrt{21}}{12\left(\sqrt{21}\right)^{2}}
Rationalize the denominator of \frac{42}{12\sqrt{21}} by multiplying numerator and denominator by \sqrt{21}.
\frac{42\sqrt{21}}{12\times 21}
The square of \sqrt{21} is 21.
\frac{\sqrt{21}}{2\times 3}
Cancel out 6\times 7 in both numerator and denominator.
\frac{\sqrt{21}}{6}
Multiply 2 and 3 to get 6.
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