\(-x^2+5x-6=0\)
\(\Leftrightarrow-\left(x^2-5x+6\right)=0\Leftrightarrow-\left(x^2-2x-3x+6\right)=0\)
\(\Leftrightarrow-\left(x-2\right)\left(x-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)
\(-x^2+5x-6=0
\)
\(\Leftrightarrow-\left(x^2-5x+6\right)=0\)
\(\Leftrightarrow-\left(x^2+2x+3x+6\right)=0\)
\(\Leftrightarrow-[\left(x^2+2x\right)+\left(3x+6\right)]=0\)
\(\Leftrightarrow-[x\left(x+2\right)+3\left(x+2\right)]=0\)
\(\Leftrightarrow-[\left(x+3\right)\left(x+2\right)]=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\x+2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-2\end{matrix}\right.\)
Vậy phương trình có 2 nghiệm là \(\left[{}\begin{matrix}x=-3\\x=-2\end{matrix}\right.\)