a≥-x²-y²-2x-2y=2-(x²+2x+1+y²+2y+1)=2-[(x+1)²+(y+1)²](x+1)²+(y+1)²≥0 恒成立,则2-[(x+1)²+(y+1)²]≤2为使 a≥-x²-y²-2x-2y,a的取值范围应该是[2,...