|a-2|+|b-1|+|c+2/3|=0
|a-2|=0
a=2
|b-1|=0
b=1
|c+2/3|=0
c=-2/3
a²+b²+c²+2ab+2ac+2bc
=2²+1²+(-2/3)²+2*2*1+2*2*(-2/3)+2*1*(-2/3)
=4+1+4/9+4-8/3-4/3
=5+4/9
=49/9
（a+b+c)²
=(2+1-2/3)²
=(7/3)²
=49/9
（a+b+c）²=a²+b²+c²+2ab+2ac+2bc