a, Vì : \(\left(x-1\right)\left(x+3\right)=0\)
\(\Rightarrow\left[\begin{matrix}x-1=0\\x+3=0\end{matrix}\right.\) \(\Leftrightarrow\left[\begin{matrix}x=0+1=1\\x=0-3=-3\end{matrix}\right.\)
Vậy x = 1 hoặc x = -3
b, \(x\left(x+2\right)-3x-6=0\Leftrightarrow x\left(x+2\right)-3x=6\)
\(\Leftrightarrow x\left(x+2-3\right)=6\Leftrightarrow x\left(x-1\right)=6\)
\(\Rightarrow x;x-1\in\left\{\pm1;\pm2;\pm3;\pm6\right\}\)
Mà : x và x - 1 là hai số tự nhiên liên tiếp \(\Rightarrow x=3\in Z\)
11) \(\left(x-1\right).\left(x+3\right)=0\)
\(\Rightarrow\left[\begin{matrix}x-1=0\\x+3=0\end{matrix}\right.\Rightarrow\left[\begin{matrix}x=-1\\x=3\end{matrix}\right.\)
(1- 1/2) . ( 1-1/3) . ( 1-1/4).............. (1-1/1999) . (1- 1/2000)
