\(3x^2+5x-8=0\)
\(\Leftrightarrow\) \(\left(3x^2-3x\right)+\left(8x-8\right)=0\)
\(\Leftrightarrow\) \(3x\left(x-1\right)+8\left(x-1\right)=0\)
\(\Leftrightarrow\) \(\left(3x+8\right)\left(x-1\right)=0\)
\(\Leftrightarrow\) \(\left[{}\begin{matrix}3x+8=0\\x-1=0\end{matrix}\right.\) \(\Leftrightarrow\) \(\left[{}\begin{matrix}3x=-8\\x-1=0\end{matrix}\right.\) \(\Leftrightarrow\) \(\left[{}\begin{matrix}x=-\frac{8}{3}\\x=1\end{matrix}\right.\)
Vậy đa thức có nghiệm \(\left[{}\begin{matrix}x=-\frac{8}{3}\\x=1\end{matrix}\right.\)