[tex]15 \sqrt{14} \div (6 \sqrt{7} - 3 \sqrt{7} ) + 2 \sqrt{10} \times (4 \sqrt{5} - 6 \sqrt{5} ) = \\ = 15 \sqrt{14} \div 3 \sqrt{7} + 2 \sqrt{10} \times ( - 2 \sqrt{5} ) = \\ = 5 \sqrt{2} - 4 \sqrt{50} = \\ = 5 \sqrt{2} - 20 \sqrt{2} = \\ = - 15 \sqrt{2} [/tex]
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