Physics GRE Discussion Forums

excuse me, but
WHAT THE F* choises (B) & (D) coincide????

S1 = S1x + S1y + S1z
S1 = S2x + S2y + S2z

Those two can't coincide... go back to your QM to the chapter about spin addition

BTW this question has to do with math more than physik

Nope, I'm not wrong. Just simplify the expression (D) to obtain (B)!
Moreover, the operator (J1+J2)^2 may have common eigenfunctions with J1^2 & J2^2 only in the ground state, that's why (B)=(D)!