Đáp án:
Giải thích các bước giải:
`a) ( x +1 )^2 - 3 ( x + 1 ) = 0`
`⇔ x^2 + 2x + 1 - 3x - 3 = 0`
`⇔ x^2 -x - 2 = 0`
`⇔ x^2 + x - 2x -2 = 0`
`⇔ x(x+1) - 2 (x+1) = 0`
`⇔ (x+1)(x-2)=0`
⇔\(\left[ \begin{array}{l}x+1=0\\x-2=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-1\\x=2\end{array} \right.\)
Vậy `x=-1; x=2`
`b) 2 ( 3x - 2 )^2 = 9x^2 - 4`
`⇔2(3x-2)^2=(3x)^2-2^2`
`⇔2(3x-2)^2=(3x-2)(3x+2)`
`⇔2(3x-2)^2-(3x-2)(3x+2)=0`
`⇔(3x-2)[2(3x-2)-(3x+2)]=0`
`⇔(3x-2)(6x-4-3x-2)=0`
`⇔(3x-2)(3x-6)=0`
⇔\(\left[ \begin{array}{l}3x-2=0\\3x-6=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}3x=2\\3x=6\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=\dfrac{2}{3}\\x=2\end{array} \right.\)
Vậy `x= 2/3; x=2`
