Trường hợp `1`
: Nếu đề là :
`8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/26 - 1/12 - 1/6 - 1/2`
Bài làm :
`8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/26 - 1/12 - 1/6 - 1/2`
`= ( 8/9 - 1/72 - 1/56 - 1/42 - 1/30) - ( 1/26 + 1/12 + 1/6 + 1/2)`
`=(2240/2520 - 35/2520- 45/2520 -60/2520 -84/2520) - (6/156 + 13/156 + 26/156 + 78/156)`
`= 4/5 - 41/52`
`= 3/260`
``
Trường hợp `2` :
Nếu đề là :
`8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2`
Bài làm :
`8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2`
`= 8/9 - ( 1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)`
`= 8/9 - ( 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72)`
`= 8/9 - ( 1/( 1.2) + 1/( 2.3) + 1/( 3.4) + 1/(4,5) + 1/( 5.6) + 1/( 6.7) + 1/( 7.8) + 1/( 8.9))`
`= 8/9 - ( 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9)`
`= 8/9 - ( 1 - 1/9)`
`=8/9 - 8/9`
`= 0`
