\[\boxed{\text{89\ (89).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ 6\sqrt{3} + \sqrt{27} - 3\sqrt{75} =\]
\[= 6\sqrt{3} + 3\sqrt{3} - 15\sqrt{3} = - 6\sqrt{3}\]
\[2)\ (\sqrt{50} - 3\sqrt{2}) \cdot \sqrt{2} =\]
\[= \sqrt{100} - 3\sqrt{4} = 10 - 3 \cdot 2 = 4\]
\[3)\ \left( 2 - \sqrt{3} \right)^{2} = 4 + 3 - 4\sqrt{3} =\]
\[= 7 - 4\sqrt{3}\]