[tex]\sqrt2+\sqrt8-3\sqrt2 = \\ \\ = \sqrt2+\sqrt{4\cdot 2}-3\sqrt2 = \\ \\ = \sqrt2+\sqrt{2^2\cdot 2}-3\sqrt2 = \\ \\ = \sqrt2+2\sqrt2-3\sqrt2 = \\ \\ =\sqrt2\cdot (1+2)-3\sqrt2 = \\ \\ =\sqrt2\cdot 3-3\sqrt2 = \\ \\ = 3\sqrt2 -3\sqrt2 = \\ \\ = 0[/tex]
