`a)`
`18x - 13 = 5x + 12`
`⇔ 18x - 5x = 12 + 13`
`⇔ 13x = 25`
`⇔ x = 25/13`
`Vậy S = { 25/13 }`
`b)`
`5(4x - 3) = 6(2x - 4)`
`⇔ 20x - 15 = 12x - 24`
`⇔ 20x - 12x = -24 + 15`
`⇔ 8x = -9`
`⇔ x = -9/8`
`Vậy S = { -9/8 }`
`c)`
`(7x - 7)(x - 12) = 0`
⇔ \(\left[ \begin{array}{l}7x - 7 = 0\\x - 12 = 0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x = 1\\x = 12\end{array} \right.\)
`Vậy S = { 1 ; 12 }`
`d)`
`(3 - x)(9 - x) = 0`
⇔ \(\left[ \begin{array}{l}3 - x = 0\\9 - x = 0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x = 3\\x = 9\end{array} \right.\)
`Vậy S = { 3 ; 9 }`
`e)`
`10x + 5 < 2x + 4`
`⇔ 10x - 2x < 4 - 5`
`⇔ 8x < -1`
`⇔ x < -1/8`
`Vậy S = { x | x < -1/8 }`
`f)`
`3x - 5 < 4x + 5`
`⇔ 3x - 4x < 5 + 5`
`⇔ - x < 10`
`⇔ x > -10`
`Vậy S = { x | x > -10 }`
