`#Sad`
`a)`
`x(x-2)+x-2 = 0`
`⇔ x(x-2)+(x-2) = 0`
`⇔ (x+1)(x-2) = 0`
`⇔` \(\left[ \begin{array}{l}x+1=0\\x-2=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-1\\x=2\end{array} \right.\)
`\text{Vậy S=}` `{-1; 2}`
`b)`
`(x-1)^2+x(4-x) = 0`
`⇔ x^2-2x+1+4x-x^2 = 0`
`⇔ (x^2-x^2)+(-2x+4x)+1 = 0`
`⇔ 2x+1 = 0`
`⇔ 2x = -1`
`⇔ x = -(1)/(2)`
`\text{Vậy S=}` `{-(1)/(2)}`
