denotes a light meson, are studied in the framework of improved instantaneous Bethe-Salpeter (BS) equation and the Mandelstam formula. The numerical results (width and branching ratio of the decays) are presented in tables, and in order to compare conveniently, those obtained by other approaches are also put in the relevant tables. Based on the fact that the ratio
BR(Bc+→J/ψπ+)BR(Bc+→ψ(2S)π+)=0.24−0.040+0.023
estimated here is in good agreement with the observation by the LHCb