1.
If z1,z2,z3∈Cz_1, z_2, z_3 \in \mathbb{C} are the vertices of an equilateral triangle whose centroid is z0z_0, then ∑k=13(zk−z0)2\displaystyle\sum_{k=1}^{3}(z_k - z_0)^2 is equal to: