Evaluate
4\sqrt{21}\approx 18.33030278
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2\times 2\sqrt{21}
Factor 84=2^{2}\times 21. Rewrite the square root of the product \sqrt{2^{2}\times 21} as the product of square roots \sqrt{2^{2}}\sqrt{21}. Take the square root of 2^{2}.
4\sqrt{21}
Multiply 2 and 2 to get 4.
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