`PIET!?A`

`c)`

`(-2/3)^2 - (x + 1/6) = 1/2`

`4/9 - (x + 1/6) = 1/2`

`x + 1/6 = 4/9 - 1/2`

`x + 1/6 = 8/18 - 9/18`

`x + 1/6 = -1/18`

`x = -1/18 - 1/6`

`x = -1/18 - 3/18`

`x = -4/18`

`x = -2/9`.

Vậy `x = -2/9`.

`d)`

`(x - 3/4) : 2/5 = 1 1/4`

`(x - 3/4) : 2/5 = 5/4`

`x - 3/4 = 5/4 . 2/5`

`x - 3/4 = 10/20`

`x - 3/4 = 1/2`

`x = 1/2 + 3/4`

`x = 2/4 + 3/4`

`x = 5/4`.

Vậy `x = 5/4`.

`e)`

`7/3 : (1/2 - 3x) = -1 3/4`

`7/3 : (1/2 - 3x) = -7/4`

`1/2 - 3x = 7/3 : (-7/4)`

`1/2 - 3x = 7/3 . (-4/7)`

`1/2 - 3x = -4/3`

`3x = 1/2 - (-4/3)`

`3x = 1/2 + 4/3`

`3x = 3/6 + 8/6`

`3x = 11/6`

`x = 11/6 : 3`

`x = 11/18`.

Vậy `x = 11/18`.

`f)`

`-5/12 : (2/3 - 1/2 x) = -2 1/2`

`-5/12 : (2/3 - 1/2 x) = -5/2`

`2/3 - 1/2 x = -5/12 : (-5/2)`

`2/3 - 1/2 x = -5/12 . (-2/5)`

`2/3 - 1/2 x = 2/12`

`2/3 - 1/2 x = 1/6`

`1/2 x = 2/3 - 1/6`

`1/2 x = 4/6 - 1/6`

`1/2 x = 3/6`

`1/2 x = 1/2`

`x = 1/2 : 1/2`

`x = 1`.

Vậy `x = 1`.