a*a+b*b>=2*a*b;
b*b+c*c>=2*b*c;
c*c+a*a>=2*c*a;
each = is true only if x==y
2(a*a+b*b+c*c)>=2(a*b+b*c+c*d)
the = is true only if
a==b==c
b*b+c*c>=2*b*c;
c*c+a*a>=2*c*a;
each = is true only if x==y
2(a*a+b*b+c*c)>=2(a*b+b*c+c*d)
the = is true only if
a==b==c