x²y²+xy-x²-y²+x+y+2=（x²y²-x²-y²+1）+（xy+x+y+1）=（x²-1）（y²-1）+（x+1)(y+1)=（x+1）（x-1）(y+1)(y-1）+（x+1)(y+1)=（x+1)(y+1)[(x-1)(y-1)+1]=（x+1)(...