I would like to know how the below can be solved. Detailed explanation would be good to have, thanks.

3. Let {(xi, yi)} are given, xi E R" and yi E R. Assume N f(a; x - bi) + Allac| |2 (3) xERn i=1 with f : R - R is a differentiable function. (a) Compute VF(x). (c) Prove the minimizer of F must be in the form of ac* = cai, with c = [C1, C2, ..., CN]T. (d) Re-express the minimization problem (3) in terms of c with fewer unknowns