X²-XY-6Y²+2X-Y+1
先配二次项
=(x-3y)(x+2y)+2x-y+1
需要x-3y 所以构造x-3y
=(x-3y)(x+2y)+x-3y+x+2y+1
=(x-3y)(x+2y+1)+x+2y+1
=(x-3y+1)(x-2y+1)
首正解
X²-XY-6Y²+2X-Y+1
先配二次项
=(x-3y)(x+2y)+2x-y+1
需要x-3y 所以构造x-3y
=(x-3y)(x+2y)+x-3y+x+2y+1
=(x-3y)(x+2y+1)+x+2y+1
=(x-3y+1)(x-2y+1)
首正解