\(x^3+4x^2+x-6\)
\(=\left(x^3-x^2\right)+\left(5x^2-5x\right)+\left(6x-6\right)\)
\(=x^2\left(x-1\right)+5x\left(x-1\right)+6\left(x-1\right)\)
\(=\left(x-1\right).\left(x^2+5x+6\right)\)
\(=\left(x-1\right)\left[\left(x^2+2x\right)+\left(3x+6\right)\right]\)
\(=\left(x-1\right)\left[x\left(x+2\right)+3\left(x+2\right)\right]\)
\(=\left(x-1\right)\left(x+2\right)\left(x+3\right)\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x-1=0\\x+2=0\\x+3=0\end{array}\right.\Leftrightarrow\left[\begin{array}{nghiempt}x=1\\x=-2\\x=-3\end{array}\right.\)
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