Evaluate
42\sqrt{5}\approx 93.914855055
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21\times 2\sqrt{5}
Factor 20=2^{2}\times 5. Rewrite the square root of the product \sqrt{2^{2}\times 5} as the product of square roots \sqrt{2^{2}}\sqrt{5}. Take the square root of 2^{2}.
42\sqrt{5}
Multiply 21 and 2 to get 42.
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