\(\left(x-1\right)\left(x+2\right)-x-2=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+2\right)-\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-2\right)=0\)
\(\rightarrow\orbr{\begin{cases}x+2=0\\x-2=0\end{cases}\leftrightarrow\orbr{\begin{cases}x=-2\\x=2\end{cases}}}\)