5/6-7/129/20-11/
5/6-7/12+9/20-11/30+13/42
=10/12-7/12+9/20-11/30+13/42
=1/4+9/20-11/30+13/42
=5/20+9/20-11/30+13/42
=7/10-11/30+13/42
=(21-11)/30+13/42
=1/3+13/42
=27/42=9/14。
5/6-7/12+9/20-11/30+13/42
=10/12-7/12+9/20-11/30+13/42
=1/4+9/20-11/30+13/42
=5/20+9/20-11/30+13/42
=7/10-11/30+13/42
=(21-11)/30+13/42
=1/3+13/42
=27/42=9/14。
收起