a²+b²+c² - 2(a+b+c) +3 =0
(a²-2a+1)+(b²-2b+1)+(c²-2c+1) =0
(a-1)² +(b-1)² +(c-1)² =0
∴a-1=0,b-1=0,c-1=0
a=b=c=1
a³+b³+c³-3abc =0