Evaluate
20\sqrt{2}-36\approx -7.715728753
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5\times 4\sqrt{2}-4\sqrt{81}
Factor 32=4^{2}\times 2. Rewrite the square root of the product \sqrt{4^{2}\times 2} as the product of square roots \sqrt{4^{2}}\sqrt{2}. Take the square root of 4^{2}.
20\sqrt{2}-4\sqrt{81}
Multiply 5 and 4 to get 20.
20\sqrt{2}-4\times 9
Calculate the square root of 81 and get 9.
20\sqrt{2}-36
Multiply -4 and 9 to get -36.
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