\(\left(\sqrt{80}-3\sqrt{2}-\sqrt{45}\right)\sqrt{2}-\sqrt{40}=\left(4\sqrt{5}-3\sqrt{2}-3\sqrt{5}\right)\sqrt{2}-2\sqrt{10}\)
\(=4\sqrt{10}-6-3\sqrt{10}-2\sqrt{10}=-6-\sqrt{10}\)
\(\left(\sqrt{28}-2\sqrt{14}+\sqrt{7}\right)\sqrt{7}+7\sqrt{8}=\left(2\sqrt{7}-2\sqrt{14}+\sqrt{7}\right)\sqrt{7}+14\sqrt{2}\)
\(=14-14\sqrt{2}+7+14\sqrt{2}=21\)
\(\dfrac{1}{\sqrt{5}-\sqrt{3}}+\dfrac{1}{\sqrt{5}+\sqrt{3}}=\dfrac{\sqrt{5}+\sqrt{3}+\sqrt{5}-\sqrt{3}}{\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}-\sqrt{3}\right)}=\dfrac{2\sqrt{5}}{5-3}=\sqrt{5}\)
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