a²+2b²+c²-2ab-4b+2c+5=0
(a-b)^2+(c+1)^2+(b-2)^2=0
a-b=0,c+1=0,b-2=0
a=b,c=-1,b=2
a=2,b=2,c=-1
a+b+c=2+2-1=3