Evaluate
-30\sqrt{7}\approx -79.372539332
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2\sqrt{7}\left(-1\right)-28\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}.
-2\sqrt{7}-28\sqrt{7}
Multiply 2 and -1 to get -2.
-30\sqrt{7}
Combine -2\sqrt{7} and -28\sqrt{7} to get -30\sqrt{7}.
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