①（√6+√8）*√3
=√18+√24
=3√2+2√6
②（4√6-3√2）/2√2
=4√6/2√2-3√2/2√2
=2√3 -3/2
③（√48-3√27）/√3
=√48/√3-3√27/√3
=√16-3√9
=4-9
=-5
④（3-√2）²
=3²-6√2+2
=11-6√2
⑤√3（√12-3√75）
=√3√12-√3×3√75
=√36-3√225
=6-3×15
=6-45
=-39
⑥（20/3√3-3√6）*18
=20/3√3×18-3√6×18
=40√3-54√6