`A=2019-|x-3,5|`
`⇒A=2019+(-|x-3,5|)`
Vì `|x-3,5|≥0` `∀x`
`⇒-|x-3,5|≤0`
`⇒A≤2019`
Dấu $"="$ xảy ra khi `|x-3,5|=0⇒x=3,5`
`B=-|1,4-x|-2020`
`⇒B=-(|1,4-x|+2020)`
Vì `|1,4-x|≥0` `∀x`
`⇒|1,4-x|+2020≥2020`
`⇒B≤-2020`
Dấu $"="$ xảy ra khi `|1,4-x|=0⇒x=1,4`