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6. Find the subset V of the space of all real valued n x n matrices defined by V ={AER"" | u(x) is harmonic = u(Ar) is harmonic}. (Reminder: a function is harmonic in R" if CO, u(x) = 0 for all r e R" ). a. Compute all possible determinants of matrices in V.b. Show that V is a group, i.e. (a) if A. B E V then AB, BA e V; (b) there exists a identity element C E V such that CA = AC = A for all A e V; (c) for each A E V there exists B E V such that AB = BA = C (the identity) and (d) the group multiplication is associative (AB) D = A(BD) for all A, B, DE V