2a²–ab-b²可以用十字相乘法进行因式分解 x²- 3ax + 2a²–ab -b²=0 x²- 3ax +（2a²–ab - b²）=0 x²- 3ax +（2a+b）（a-b）=0 1 -b 2 ╳ +b [x-（2a+b）][ x-（a-b）]...