1. The problem statement and attempt at solution Given the matrix S_ij and a_i evaluate a),b),c),d) and e) For a) I think i use Einsteins convention. b) I just first sum on i, and then on j giving me 9 terms. The answer I get is 24. d) can i change m with i since they are both dummy indexes? e) the same problem as d I guess, is this allowed? I'm trying to learn continuum mechanics by my self, and this is the first step. Thank you.