Question

3V10x(V2-2V5)-2V10x(4V2-7V5)
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Answer 1

$3 \sqrt{10} \times ( \sqrt{2 } - 2 \sqrt{5} ) - 2 \sqrt{10} \times (4 \sqrt{2} - 7 \sqrt{5} ) = \\ = 3 \sqrt{20} - 6 \sqrt{50} - 8 \sqrt{20} + 14 \sqrt{50} = \\ = - 5 \sqrt{20} + 8 \sqrt{50} = \\ = - 5 \times 2 \sqrt{5} + 8 \times 5 \sqrt{2} = \\ = - 10 \sqrt{5} + 40 \sqrt{2} = 40\sqrt{2} - 10 \sqrt{5} = 10 \times (4\sqrt{2} - \sqrt{5} )$