2a²-5a-8-(a+3)(a-3)+5(a-2)=2(a-2)(a-3)
(=)2a²-5a-8-(a+3)(a-3)+5(a-2)-2(a-2)(a-3)=0
(=)2a²-5a-8-a²+9+5a-10-2(a²-3a-2a+6)=0
(=)2a²-5a-8-a²+9+5a-10-2(a²-5a+6)=0
(=)2a²-5a-8-a²+9+5a-10-2a²+10a-12=0
(=)-a²+10a-21=0
(=)-a²+3a+7a-21=0
(=)-a(a-3)+7(a-3)=0
(=)(-a+7)(a-3)=0
(=)\(\left[ \begin{array}{l}-a+7=0\\a-3=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}-a=-7\\a=3\end{array} \right.\) (=)\(\left[ \begin{array}{l}a=7\\a=3\end{array} \right.\)
