Evaluate
\sqrt{2}-2\sqrt{7}\approx -3.87728906
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\sqrt{2}-2\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}.
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