1. The problem statement, all variables and given/known data [S2 total, Sz ∅1] 2. Relevant equations S2 total = S2∅1+ 1∅S2+2(Sx∅Sx+Sy∅Sy+ Sz∅Sz) 3. The attempt at a solution I calculated it in steps: (1∅Sx 2 +Sx 2∅1) * Sz ∅1 =[S2x, Sz] ∅1 + Sz∅Sx 2 =-h_cut i (SxSy+SySx)∅1 + Sz∅Sx 2 Is it correct way of doing it? I mean I just did one small segment of it. There is still a lot of calculation to be done. Is there any short method?