Evaluate
-7\sqrt{5}\approx -15.652475842
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-3\times 2\sqrt{5}-\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}.
-6\sqrt{5}-\sqrt{5}
Multiply -3 and 2 to get -6.
-7\sqrt{5}
Combine -6\sqrt{5} and -\sqrt{5} to get -7\sqrt{5}.
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