2b=2×b
3a²=3×a×a
6abc=2×3×a×b×c
公分母是:2×3×a×a×b×c=6a²bc

a/2b
=[a(3a²c)]/[(2b)(3a²c)]
=3a³c/6a²bc

1/3a²
= 2bc/[(3a²)(2bc)]
=2bc/6a²bc

-5/6abc
=-5a/[(6abc)a]
=-5a/6a²bc