x3 là x mũ 3 hay x nhân 3
4x2 là 4 nhân x nhân 2 hay 4 nhân 2 hay 4 mũ 2 ???
Ta có: \(x^3+4x^2+x-6=0\)
\(\Leftrightarrow x^3+3x^2+x^2+3x-2x-6=0\)
\(\Leftrightarrow x^2\left(x+3\right)+x\left(x+3\right)-2\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2+x-2\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2+2x-x-2\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left[x\left(x+2\right)-\left(x+2\right)\right]=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+2\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\x+2=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-2\\x=1\end{matrix}\right.\)
Vậy: Tập nghiệm S={-3;-2;1}
