Có \(x^3+4x^2+5x+2=\left(x+1\right)\left(x^2+ax+b\right)\)
\(\Leftrightarrow x^3+4x^2+5x+2=x^3+x^2\left(a+1\right)+x\left(a+b\right)+b\)
Cân bằng hệ số: \(\left\{{}\begin{matrix}a+1=4\\a+b=5\\b=2\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}a=3\\b=2\end{matrix}\right.\)
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