$$\sqrt{2}+\sqrt{8}+\sqrt{18} \\$$ $$=\sqrt{2}+\sqrt{4\times2}+\sqrt{9\times2} \\$$ $$=\sqrt{2}+\sqrt{4}\sqrt{2}+\sqrt{9}\sqrt{2}=\sqrt{2}+2\sqrt{2}+3\sqrt{2} \\$$ $$=6\sqrt{2}$$