Question

把（X-Y)当成一个因式，合并2*（X-Y)的平方-3*（X-Y)+5(X-Y)的平方+4*(X-Y)中的同类项

Answer 1

（x-y)^2+3（x-y)-2（x-y）^2

=[(x-y)^2-2(x-y)^2]+3(x-y)

=-(x-y)^2+3(x-y)