`7)` `{x-3}/5={-4}/10`

`(x-3).10=-4.5`

`(x-3).10=-20`

`x-3=-2`

`x=1`

Vậy `x=1`

`8)` `27/{-6}={-9}/{x+12}`

`27. (x+12)=(-9).(-6)`

`27. (x+12)=54`

`x+12=2`

`x=-10`

Vậy `x=-10`

`9)` `{x+2}/{-2}={-9}/{x+2}`

`(x+2)^2=(-2).(-9)`

`(x+2)^2=18`

`(x+2)^2=` `(` `+-` `9)^2`

TH1:

`x+2=-9`

`x=-11`

TH2:

`x+2=9`

`x=7`

Vậy `x in {-11 ; 7}`

`10)` `2/5 x -1/10 x = 1`

`(2/5-1/10)x=1`

`3/10 x=1`

`x=1: 3/10`

`x=10/3`

Vậy `x=10/3`

`11)` `3/7 x + 1/14 x - 8/14 = 1 2/7`

`(3/7 + 1/14) x - 8/14=9/7`

`1/2 x - 8/14=9/7`

`1/2 x= 13/7`

`x=26/7`

Vậy `x=26/7`

`12)` `(1/2 - x)^2 - 1={-9}/25`

`(1/2 - x)^2 = 16/25`

`(1/2 - x)^2 =` `(` `+-` `4/5)^2`

TH1:

`1/2 - x=-4/5`

`x=13/10`

TH2:

`1/2 - x=4/5`

`x=-3/10`

Vậy `x in {13/10 ; -3/10}`