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1减6分之1加42分之1加56分之1加72分之1=

来源:学生作业帮 编辑:拍题作业网作业帮 分类:数学作业 时间:2024/04/28 22:53:25
1减6分之1加42分之1加56分之1加72分之1=
2乘4分之2加4乘6分之2加6乘8分之2加8乘10分之2=
5乘9分之4加9乘13分之4加13乘17分之4加17乘21分之4=
1题:
1-1/6+1/42+1/56+1/72
=1-1/6+(1/42+1/56+1/72)
=1-1/6+[(1/6-1/7)+(1/7-1/8)+(1/8-1/9)]
=1-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1-1/9
=8/9
2题:
2/(2×4)+2/(4×6)+2/(6×8)+2/(8×10)
=(1/2-1/4)+(1/4-1/6)+(1/6-1/8)+(1/8-1/10)
=1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10
=1/2-1/10
=5/10-1/10
=2/5
3题:
4/(5×9)+4/(9×13)+4/(13×17)+4/(17×21)
=(1/5-1/9)+(1/9-1/13)+(1/13-1/17)+(1/17-1/21)
=1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21
=1/5-1/21
=21/105-5/105
=16/105