找规律计算1.2.3.4

1、2[(1／1-1／2)+(1／2-1／3)+、、、+(1／99-1／100)]
=2(1-1／100)=99／50
2、[1／3+(1／3-1／5)／2+(1／5-1／7)／2+(1／21-1／23)／2]
=1／3+(1／3-1／23)／2
=1／2-1／23=21／46
3、1／3+1／4-1／4-1／5-1／5-1／6-1／6-1／7-1／7-1／8-1／8-1／9
=1／3-2／5-1／3-2／7-1／4-1／9
=-24／35-13／36
=-1319／1260
4、3／2×5／4×7／6×9／8×11／10×2／3×4／5×6／7×8／9
=11／10