`\text{1)}`
`5x(1/5x -2) + 3(6 -1/3x^2) =12`
`-> x^2 - 10x + 18 - x^2 =12`
`-> (x^2 -x^2) - 10x +18 =12`
`-> -10x = -6`
`-> x = 3/5`
Vậy `S = {3/5}`
$\\$
`\text{2)}`
`3x(4/3x+1) -4x(x-2) =10`
`-> 4x^2 + 3x - 4x^2 +8x =10`
`-> (4x^2 -4x^2) + (3x+8x) =10`
`-> 11x =10`
`-> x =10/11`
Vậy `S = {10/11}`
$\\$
`5(x^2 -3x+1) + x(1-5x) =x-2`
`-> 5x^2 - 15x +5 +x - 5x^2 = x -2`
`-> (5x^2 -5x^2) + (-15x +x -x ) = -2 -5`
`-> -15x = -7`
`-> x = 7/15`
Vậy `S = {7/15}`
