[tex]3\sqrt2\cdot(5\sqrt6-7\sqrt3)=3\cdot5\cdot\sqrt{2\cdot6}-3\cdot7\cdot\sqrt{2\cdot3}\\\\=15\sqrt{12}-21\sqrt6=15\sqrt{4\cdot3}-21\sqrt6=15\cdot\sqrt4\cdot\sqrt3-21\sqrt6\\\\=15\cdot2\cdot\sqrt3-21\sqrt6=\boxed{30\sqrt3-21\sqrt6}[/tex]
[tex]Used:\\\sqrt{a}\cdot\sqrt{b}=\sqrt{a\cdot b}[/tex]
