1,（x-y+3)^2>=0,√2-y>=0,所以只有（x-y+3)^2=0,√2-y=0
于是x-y+3=0,2-y=0,解得y=2,x=-1
x+y=1;
2,展开得a^2+2a-3+a^2-2a=2a^2-3