Bài làm :
`(x+1)^2 = 0`
`⇔(x+1)(x+1)=0`
`⇔x(x+1)+1(x+1)=0`
`⇔x^2 +1x+1(x+1)=0`
`⇔x^2 +1+x+1=0`
`⇔x=-1`
Vậy `x=-1`
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`x(x-5)=0`
⇔ \(\left[ \begin{array}{l}x=0\\x-5=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=0\\x=5\end{array} \right.\)
Vậy `x∈{0;5}`
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`( 2x + 4) . ( 3x + 3) = 0`
⇔ \(\left[ \begin{array}{l}2x +4 = 0\\3x + 3 = 0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}2x=-4\\3x=-3\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=-2\\x=-1\end{array} \right.\)
Vậy `x ∈ { -2 ; -1 }`
