由0<θ<π/2得tanθ>0.由z=3 cos⁡θ+i⁡2 sin⁡θ，得0<arg⁡z<π/2及tan⁡(arg⁡z )=(2 sin⁡θ)/(3 cos⁡θ )=2/3 tan⁡θ.故tan⁡= tan⁡(θ-arg⁡z )==,∵3/tan⁡θ +2 tan⁡θ≥2∴≤/12...