Evaluate
3\left(2\sqrt{2}-21\right)\approx -54.514718626
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2\times 3\sqrt{2}-7\sqrt{81}
Factor 18=3^{2}\times 2. Rewrite the square root of the product \sqrt{3^{2}\times 2} as the product of square roots \sqrt{3^{2}}\sqrt{2}. Take the square root of 3^{2}.
6\sqrt{2}-7\sqrt{81}
Multiply 2 and 3 to get 6.
6\sqrt{2}-7\times 9
Calculate the square root of 81 and get 9.
6\sqrt{2}-63
Multiply -7 and 9 to get -63.
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