Bài 1:
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 $x=0$ hoặc `x=3`
b) $x(x+9)=0$
\(⇒\left[ \begin{array}{l}x=0\\x+9=0\end{array} \right.\)
\(⇒\left[ \begin{array}{l}x=0\\x=-9\end{array} \right.\)
Vậy $x=0$ hoặc `x=-9`
c) $(x+1)(x-1)=0$
\(⇒\left[ \begin{array}{l}x+1=0\\x-1=0\end{array} \right.\)
\(⇒\left[ \begin{array}{l}x=-1\\x=1\end{array} \right.\)
Vậy $x=-1$ hoặc `x=1`
d) $(x-13)(x^2+8)=0$
`⇒x-13=0` (do `x^2+8>0∀x)`
`⇒x=13`
Vậy $x=13$
