3/2-5/6+7/12-9/20+11/30-13/42 = = = 简便算

3/2-5/6+7/12-9/20+11/30-13/42 = = = 简便算
3/2-5/6+7/12-9/20+11/30-13/42 = = = 简便算

3/2-5/6+7/12-9/20+11/30-13/42 = = = 简便算
3/2-5/6+7/12-9/20+11/30-13/42
=3/2+7/12-9/20+11/30-13/42-5/6
=18/12+7/12-27/60+22/60-13/42-35/42
=25/12-5/60-48/42
=25/12-1/12-8/7
=2-8/7
=6/7

解:原式=3/2-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=3/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1-1/7
=6/7