Hi Yanika, Please try ?uniroot and ?ployroot f <- function(x) x^4-16 uniroot(f, lower= -3, upper=0) polyroot(c(-16,0,0,0,1)) ----- A R learner. -- View this message in context: http://r.789695.n4.nabble.com/non-linear-fourth-order-differential-equations-tp3062805p3062894.html Sent from the R help mailing list archive at Nabble.com.