Bài làm
a) x( 2 + x )( 7 - x ) = 0
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\2+x=0\\7-x=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-2\\x=7\end{matrix}\right.\)
Vậy x = 0 hoặc x = -2 hoặc x = 7
b) ( x - 1 )( x + 2 )( x - 3 ) = 0
\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x+2=0\\x-3=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-2\\x=3\end{matrix}\right.\)
Vậy x = 1 hoặc x = -2 hoặc x = 3
c) ( x - 5 )( x2 - 81 ) = 0
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x^2-81=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x^2=81\Leftrightarrow x=\pm9\end{matrix}\right.\)
Vậy x = 5 hoặc x = \(\pm\) 9 .
# Học tốt #
a) \(x\left(2+x\right)\left(7-x\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=0\\2+x=0\\7-x=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=-2\\x=7\end{matrix}\right.\)
Vậy \(x\in\left\{0;-2;7\right\}\)
b) \(\left(x-1\right)\left(x+2\right)\left(x-3\right)=0\\ \Rightarrow\left[{}\begin{matrix}x-1=0\\x+2=0\\x-3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=1\\x=-2\\x=3\end{matrix}\right.\)
Vậy \(x\in\left\{1;-2;3\right\}\)
c) \(\left(x-5\right)\left(x^2-81\right)=0\\ \Rightarrow\left[{}\begin{matrix}x-5=0\\x^2-81=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\x^2=81\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\x=9\\x=-9\end{matrix}\right.\)
Vậy \(x\in\left\{5;9;-9\right\}\)
