Bài 1:
`a)` Cho `A(x) = 4x - 12`
Mà `A(x) = 0`
`=> 4x - 12= 0`
`<=> 4x = 12`
`<=> x = 3`
Vậy...
`b)` Cho `B(x) = |x - 1| - 1`
Mà `B(x) = 0`
`=> |x - 1| - 1 = 0`
`<=> |x - 1| = 1`
`<=>` \(\left[ \begin{array}{l}x-1 = 1\\x-1 = -1\end{array} \right.\)
`<=> `\(\left[ \begin{array}{l}x=2\\x=0\end{array} \right.\)
Vậy...
c) Cho `C(x) = (x+1)(4-x)`
Mà `C(x) = 0`
`=> (x+1)(4-x) = 0`
`<=> ` \(\left[ \begin{array}{l}x+1 = 0\\4-x = 0\end{array} \right.\)
`<=> ` \(\left[ \begin{array}{l}x=-1\\x=4\end{array} \right.\)
Vậy..
