1. The problem statement, all variables and given/known data Show that when tree identical quadrupole phonons (boson) are coupled togheter, only states with total angular momentum 0,2,4 and 6 are allowed. 3. The attempt at a solution I know "how" to do it, but i do not know how to couple three angular momenta. In the case of two, following is true for the total: [tex] \vert j_1 - j_2\vert \leq J \leq \vert j_1 + j_2\vert [/tex] But how to do a similiar thing when there is three? Shall I look up how the triangular inequality works for three vectors?