\(\left(\sqrt{18}+\sqrt{20}-\sqrt{8}\right)\sqrt{2}-2\sqrt{10}\\ =\left(3\sqrt{2}+2\sqrt{5}-2\sqrt{2}\right)\sqrt{2}-2\sqrt{10}\\ =6+2\sqrt{10}-4-2\sqrt{10}=2\)
\(\left(\sqrt{18}+\sqrt{20}-\sqrt{8}\right)\sqrt{2}-2\sqrt{10}=\left(3\sqrt{2}+2\sqrt{5}-2\sqrt{2}\right)\sqrt{2}-2\sqrt{10}=6+2\sqrt{10}-4-2\sqrt{10}=2\)
\(\left(\sqrt{18}+\sqrt{20}-\sqrt{8}\right)\sqrt{2}-2\sqrt{10}=6+2\sqrt{10}-4-2\sqrt{10}=2\)
Ta có: \(\left(\sqrt{18}+\sqrt{20}-\sqrt{8}\right)\cdot\sqrt{2}-2\sqrt{10}\)
\(=\left(3\sqrt{2}-2\sqrt{2}+2\sqrt{5}\right)\cdot\sqrt{2}-2\sqrt{10}\)
\(=2\)