Evaluate
3\sqrt{5}\approx 6.708203932
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7\sqrt{5}-2\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}.
7\sqrt{5}-4\sqrt{5}
Multiply -2 and 2 to get -4.
3\sqrt{5}
Combine 7\sqrt{5} and -4\sqrt{5} to get 3\sqrt{5}.
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