` 3x(x - 1) + x - 1 = 0 `
` <=> 3x(x - 1) + 1(x - 1) = 0 `
` <=> (x - 1)(3x + 1) = 0 `
` <=> ` \(\left[ \begin{array}{l}x-1=0\\3x+1=0\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=0+1\\3x=0-1\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=1\\3x=-1\end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}x=1\\x=\frac{-1}{3}\end{array} \right.\)
Vậy ` x = 1 ` hoặc ` x = -1/3 `
