Simplify the expressions:
1)
[tex]3\sqrt{3}-\sqrt{3}=\sqrt{3}\cdot(3-1)=\sqrt{3}\cdot2=2\cdot\sqrt{3}[/tex]
2)
[tex]\begin{gathered} 3\cdot\sqrt{20}+3\cdot\sqrt{45}=3\sqrt{4\cdot5}+3\cdot\sqrt{9\cdot5}=3\sqrt{4}\sqrt{5}+3\sqrt{9}\sqrt{5} \\ 3\cdot2\cdot\sqrt{5}+3\cdot3\cdot\sqrt{5} \\ 6\sqrt{5}+9\sqrt{5} \\ 15\sqrt{5} \end{gathered}[/tex]
3)
[tex]\begin{gathered} -3\sqrt{54}-3\sqrt{6} \\ -3\sqrt{9\cdot6}-3\sqrt{6} \\ -3\sqrt{9}\sqrt{6}-3\sqrt{6} \\ -3\cdot3\cdot\sqrt{6}-3\sqrt{6} \\ -9\sqrt{6}-3\sqrt{6} \\ -12\sqrt{6} \end{gathered}[/tex]
4)
[tex]\begin{gathered} -2\sqrt{6}-2\sqrt{6} \\ (-2-2)\sqrt{6} \\ -4\sqrt{6} \end{gathered}[/tex]
