`A=|x-1/7|-|x+3/5|+4/5`
`=>A=(x-1/7)-(x+3/5)+4/5` ( giá trị tuyệt đối )
`=>A=(x-1/7)-(x+3/5+4/5)`
`=>A=(x-1/7)-(x+7/5)`
`=>A=x-(7/5-1/7)`
`=>A=x-44/35`
*Áp dụng : `(x-a)-(x+b)=x-(b-a)` hoặc `x-(a-b)`
`B=|-x+1/7||-x+3/5|-2/6`
`=>B=(x+1/7)(x+3/5)-2/6`
`=>B=x(1/7+3/5)-1/3`
`=>B=26/35x-1/3`