a, `x + 3/21 = 8/7`
`x + 1/7 = 8/7`
`x = 8/7 - 1/7`
`x = 1`
Vậy `x=1`
b, `|x+2| - 1/3 = 5/6`
`|x+2| = 5/6 + 2/6`
`|x+2| = 7/6`
`=>` \(\left[ \begin{array}{l}x+2=\frac{7}{6}\\x+2=\frac{-7}{6}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\frac{-5}{6}\\x=\frac{-19}{6}\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=\frac{-5}{6}\\x=\frac{-19}{6}\end{array} \right.\)
c, `4/5 - 1/3 . ( x + 3/2 ) = 7/15`
`1/3 . ( x + 3/2 ) = 4/5 - 7/15`
`1/3 . ( x + 3/2 ) = 1/3`
`x + 3/2 = 1`
`x = -1/2`
Vậy `x=-1/2`
