三式相加a²+2b+b²-2c+c²-6a=-11a²+2b+b²-2c+c²-6a+11=0(a-3)²+（b+1）²+（c-1）²=0a-3=0 b+1=0 c-1=0a=3,b=-1,c=1a+b+c=3-1+1=3
