`a)|x|>=0`
`=>|x|+1997>=1997`
`=>A<=1996/1997`
Dấu "=" xảy ra khi `x=0`
`b)|x|>=0`
`=>|x|+1996>=1996`
`=>-(|x|+1996)<=-1996`
`=>B<=-1996/1997`
Dấu "=" xảy ra khi `x=0`.
`c)c=-|x+4/7|+12/19`
Vì `|x+4/7|>=0`
`=>-|x+4/7|<=0`
`=>C<=12/19`
Dấu "=" xảy ra khi `x=-4/7`