\(-4,5x^2+72x+162=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-18\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\x-18=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=18\end{matrix}\right.\)
\(-4,5x^2+72x+162=0\\ \Leftrightarrow x^2-16x-36=0\\ \Leftrightarrow x^2+2x-18x-36=0\\ \Leftrightarrow\left(x^2+2x\right)-\left(18x+36\right)=0\\ \Leftrightarrow x\left(x+2\right)-18\left(x+2\right)=0\\ \Leftrightarrow\left(x-18\right)\left(x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-18=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=18\\x=-2\end{matrix}\right.\)
Vậy phương trình có tập nghiệm \(S=\left\{18;-2\right\}\)
