解：9/12-(8/19-5/12)=9/12-8/19+5/12=9/12+5/12-8/19=7/6-8/19=133/114-48/114=85/114
85/144
9/12-(8/19-5/12)＝9/12-8/19+5/12＝7/6-8/19＝7×19/6×19-8×6/19×6＝(7×19-8×6)/6×19
