`a, -2/3x + 1,2 = (-1/2)^{2}`
`-2/3x + 6/5 = 1/4`
`-2/3x = 1/4 - 6/5`
`-2/3x = -19/20`
`x = -19/20 : {-2}/3`
`x = 57/40`
$\text{Vậy}$ `x = 57/40`
_________________
`b, |x + 5/6| - 3/4 = 0`
`|x + 5/6| = 0 + 3/4`
`|x + 5/6| = 3/4`
$\text{TH1:}$
`x + 5/6 = 3/4`
`x = 3/4 - 5/6`
`x = -1/12`
$\text{TH2:}$
`x + 5/6 = -3/4`
`x = -3/4 - 5/6`
`x = -19/12`
$\text{Vậy}$ `x \in {-1/12 ; -19/12}`
