2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/150552We perform a systematic WKB expansion to all orders for a one--dimensional system with potential $V(x)=U_0/\cos^2{(αx)}$. We are able to sum the series to the exact energy spectrum. Then we show that any finite order WKB approximation fails to predict the individual energy levels within a vanishing fraction of the mean energy level spacing.11 pages, latex, no figures, Preprint CAMTP/96-5, July 1996, submitted to J. Phys. A: Math. GenChaotic Dynamicstext