Let `z_1 and z_2` be theroots of the equation `z^2+az+b=0` z being complex. Further, assume that the origin `z_1 and z_2` form an equilateral triangle then (A) `a^2=4b` (B) `a^2=b` (C) `a^2=2b` (D) `a^2=3b`