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▪В80.

$( \sqrt{8} - 2 \sqrt{5} )( \sqrt{2} + \sqrt[6]{20} )(2 - 2 \times \sqrt[6]{2.5} + \sqrt[3]{20} ) = (2 \sqrt{2} - 2 \sqrt{5} )( \sqrt{2} + \sqrt[6]{20} )(2 - 2 \times \sqrt[6]{ \frac{5}{2} } + \sqrt[3]{20} ) = (2 \sqrt{2} - 2 \sqrt{5} )( {( \sqrt{2} )}^{3} + {( \sqrt[6]{20} )}^{3} = (2 \sqrt{2} - 2 \sqrt{5} )( 2\sqrt{2} + \sqrt{20} ) = (2 \sqrt{2} - 2 \sqrt{5} )( 2\sqrt{2} + 2 \sqrt{5} ) = {(2 \sqrt{2} )}^{2} - {(2 \sqrt{5}) }^{2} = 4 \times 2 - 4 \times 5 = 8 - 20 = - 12$
▪В81.

$( \sqrt{27} + 3 \sqrt{2} )( \sqrt{3} - \sqrt[6]{18} )(3 + 3 \times \sqrt[6]{ \frac{2}{3} } + \sqrt[3]{18} ) = (3 \sqrt{3} + 3 \sqrt{2} )( {( \sqrt{3} )}^{3} - {( \sqrt[6]{18} )}^{3} ) = (3 \sqrt{3} + 3 \sqrt{2} )(3 \sqrt{3} - \sqrt{18} ) = (3 \sqrt{3} + 3 \sqrt{2} )(3 \sqrt{3} - 3\sqrt{2} ) = {(3 \sqrt{3}) }^{2} - {(3 \sqrt{2}) }^{2} = 9 \times 3 - 9 \times 2 = 27 - 18 = 9$