@isa
`a. ( x-7) + 11 = 3`
`⇔ x - 7 = 3 - 11`
`⇔ x - 7 = - 8`
`⇔ x = -8 + 7`
`⇔ x = -1`
Vậy `x = -1`
`b. ( x+8) . ( x² -16) =0`
`⇔ (x + 8) . (x - 4). (x + 4) = 0`
`⇔` \(\left[ \begin{array}{l}x + 8=0\\x-4=0\\x +4=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-8\\x=4\\x=-4\end{array} \right.\)
Vậy `x ∈ { -8 ; 4 ; -4}`
`c, 4.( x-6) -5.( x-2)= -7`
`⇔ 4x - 24 - 5x + 10 = -7`
`⇔ -x -14 = -7`
`⇔ -x = 7`
`x = -7`
Vậy `x = -7`