Question

If ∑vector a_i for i ∈ [i=1, n] = 0 where |a_i| = 1 ∀_i ∈ n ∈ N, then the value of ∑∑a_i . a_j for i ∈ [i=1,n], for j ∈ [j=1, n] is

(A) −n/2 

(B) −n 

(C) n/2 

(D) n

Answer 1

Answer is (A) −n/2