`|x-2015|+|x-2016|+|x-2017|`
`text{Áp dụng tính chất}` `|A|+|B|>=|A+B|`
`|x-2015|+|x-2017|`
`=|x-2015|+|2017-x|>=|x-2015+2017-x|=2`
`text{Dấu = xảy ra khi}`
`(x-2015)(2017-x)>=0`
`<=>(x-2015)(x-2017)<=0`
`<=2015<=x<=2017`
`+)|x-2016|>=0`
`text{Dấu = xảy ra khi x=2016}`
`=>A>=2`
`text{Dấu = xảy ra khi x=2016}`