我用x^2表示x的平方x^2y^2+xy-x^2-y^2+x+y+2=x^2y^2-x^2-y^2+1+xy+x+y+1=(x^2-1)(y^2-1)+(x+1)(y+1)=(x+1)(x-1)(y+1)(y-1)+(x+1)(y+1)=(x+1)(y+1)(xy-x-y+1)+(x+1)(y+1)=(x+1)(y+1)(xy-x-y+2)