a. $x.(x+3) = 0 $
⇒ \(\left[ \begin{array}{l}x=0\\x+3=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=0\\x=-3\end{array} \right.\)
Vậy $x=-3$ hoặc $x=0$
b. $ (x+2) (5-x) = 0 $
⇒ \(\left[ \begin{array}{l}x+2=0\\5-x=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=-2\\x=5\end{array} \right.\)
Vậy $x=-2$ hoặc $x=5$
c. $(x+1) (x²+ 1) = 0$
⇒ \(\left[ \begin{array}{l}x+1=0\\x^2+1=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=-1\\x^2=-1(vô lí)\end{array} \right.\)
⇒ $x=-1$
Vậy $x=-1$
