Evaluate
\frac{\sqrt{7}}{21}\approx 0.125988158
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\frac{1}{2\sqrt{7}+\sqrt{7}}
Factor 28=2^{2}\times 7. Rewrite the square root of the product \sqrt{2^{2}\times 7} as the product of square roots \sqrt{2^{2}}\sqrt{7}. Take the square root of 2^{2}.
\frac{1}{3\sqrt{7}}
Combine 2\sqrt{7} and \sqrt{7} to get 3\sqrt{7}.
\frac{\sqrt{7}}{3\left(\sqrt{7}\right)^{2}}
Rationalize the denominator of \frac{1}{3\sqrt{7}} by multiplying numerator and denominator by \sqrt{7}.
\frac{\sqrt{7}}{3\times 7}
The square of \sqrt{7} is 7.
\frac{\sqrt{7}}{21}
Multiply 3 and 7 to get 21.
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