A Study of the Decay D0->K+pi-

Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay $D^0\to K^+\pi^-$ with a signal yield of $149\pm31$ events compared to a similarly cut sample consisting of $36760 \pm 195$ $D^0\to K^-\pi^+$ events. We use the observed ratio of $D^0\to K^+\pi^-$ to $D^0\to K^-\pi^+$ $(0.404\pm 0.085\pm 0.025)$ to obtain a relationship between the $D^0$ mixing and doubly Cabibbo suppressed decay parameters.