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Đáp án:

 `26)B`

`27)B`

`28)A`

`29)B`

Giải thích các bước giải:

 Câu `26)`

`3/5+2/5:x=0`

`=>2/5:x=-3/5`

`=>x=2/(5):(-3)/5=2/(5).(-5)/3=-2/3`

`=>B`

Câu `27)`

`2/3:x-1/2=1`

`=>2/3:x=1+1/2=3/2`

`=>x=2/3:(3)/2=2/(3).(2)/3=4/9=>B`

Câu `28)`

`(x+3)/2021+(x+2)/2022+(x+1)/2023=-3`

`=>(x+3)/2021+1+(x+2)/2022+1+(x+1)/2023+1=-3+3`

`=>(x+3+2021)/2021+(x+2+2022)/2022+(x+1+2023)/2023=0`

`=>(x+2024)/2021+(x+2024)/2022+(x+2024)/2023=0`

`=>(x+2024)(1/2021+1/2022+1/2023)=0`

Vì `:`

`1/2021+1/2022+1/2023\ne0`

`=>x+2024=0=>x=-2024=>A`

Câu `29)`

`-8/15<x/40<-7/15`

`=>(-64)/120<(3x)/120<(-56)/120`

`=>(-64)<3x<-56`

`=>3x in{-63;-62;...;-57}`

Mà `x inZZ`

`=>3x in{-63;-60;..;-57}`

`=>x in{-21;-20;-19}=>B`

`@nguyen``nam500#hoidap247`