|a|=3,|b|=4,|c|=4
a+b+c=0
To find :a.b+b.c+c.a
a+b+c=0
(a+b+c).(a+b+c)=0
|a|^2+|b|^2+|c|^2 + 2(a.b+b.c+c.a)=0
9+16+16+2(a.b+b.c+c.a)=0
(a.b+b.c+c.a)=-41/2