(x-y)的平方-2(x+y) ( y-x)+3(x-y)

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

没有题意，只能分类揣测了。
1.求展开式
(x-y)的平方-2(x+y) ( y-x)+3(x-y)
=x^2-2xy+y^2-2y^2+2x^2+3x-3y
=3x^2-y^2-2xy+3x-3y
2.因式分解
(x-y)的平方-2(x+y) ( y-x)+3(x-y)
=(x-y)[(x-y)+2(x+y)+3]
=(x-y)(3x+y+3)

3X2-Y2-2XY+3X-3Y

(x-y)的平方-2(x+y) ( y-x)+3(x-y)
=(x-y)[x-y+2(x+y)+3]
=(x-y)(3x+y+3)