原式=x²-2（y+1）x+3y²-2y+3
=x²-2（y+1）x+y²+2y+1+2y²-4y+2
=x²-2（y+1）x+（y+1）²+2（y-1）²
=（x-y-1）²+2（y-1）²．
∴原式大于或等于0．
故本题答案为：大于或等于0．