把(x-y),(a+b)作为一个因式,合并同类项:3(x-y)-9(x-y)-8(x-y）＋6（x－y）－1
问题描述：
把(x-y),(a+b)作为一个因式,合并同类项:3(x-y)-9(x-y)-8(x-y）＋6（x－y）－1
答
(1)3(x-y)^2-9(x-y)-8(x-y)^2+6(x-y)-1
=(3-8)(x-y)²-(9-6)(x-y)-1
=-5(x-y)²-3(x-y)-1