a) `0,5 + 1/3 + 0,4 + 5/7 +1/6 - 4/35`
`= 1/2 + 1/3 + 2/5 + 5/7 +1/6 - 4/35`
`= (1/2 + 1/3 +1/6) +(2/5 + 5/7- 4/35)`
`= (3/6 + 2/6 +1/6) +(14/55 + 25/35 - 4/35)`
`= 1 + 1`
`= 2`
b) `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 +1/72 - (1/(7.8) + 1/(6.7) + 1/(5.6) +1/(4.5) + 1/(3.4) + 1/(2.3) + 1/(1.2))`
`= 8/9 +1/72 - ( 1/(1.2) + 1/(2.3) + 1/(3.4) + 1/(4.5) + 1/(5.6) +1/(6.7) +1/(7.8))`
`= 8/9 +1/72 - (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)`
`= 8/9 +1/72 - (1-1/8)`
`= 8/9 +1/72 - 7/8`
`= 64/72 +1/72 - 63/72`
`= 2/72`
`= 1/36`
(Chúc bạn học tốt)
