2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/92260The treatment of anharmonic oscillators (including double-wells) by instanton methods is wellknown. The alternative differential equation method is not so wellknown. Here we reformulate the latter completely parallel to the strong coupling case of the cosine potential and Mathieu equation for which extensive literature and monographs exist.Revised, minor corrections, calculations shifted to appendices, references addedQuantum PhysicsMesoscale and Nanoscale PhysicsHigh Energy Physics - Theorytext