\(x^3-7x-6=0\)
\(\Leftrightarrow x^3+x^2-x^2-6x-x-6=0\)
\(\Leftrightarrow\left(x^3+x^2\right)-\left(x^2+x\right)-\left(6x+6\right)=0\)
\(\Leftrightarrow x^2\left(x+1\right)-x\left(x+1\right)-6\left(x+1\right)=0\)
\(\Leftrightarrow\left(x^2-x-6\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[x\left(x-3\right)+2\left(x-3\right)\right]\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-3\right)\left(x+1\right)=0\)
\(\left[\begin{array}{nghiempt}x+2=0\\x-3=0\\x+1=0\end{array}\right.\Leftrightarrow\left[\begin{array}{nghiempt}x=-2\\x=3\\x=-1\end{array}\right.\)
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