Não disponível

Our objective in this work is to consider three problems related to retarded functional differential equations, using ideas and results mainly contained in recent Rybakowski's papers. First, we are interested in the search of positive solutions for a certain class of retarded functional differential equations. For this, we use an argument closely related to the WaZewski's Principle, but we don't employ Rybakowski's results in a direct way. Secondly, we investigate the existence of bounded solutions, whose derivatives are of exponential growth at infinity, of retarded functional differential of continuous type as: {x = y y = a(t)y + b(t)x(t-r) + f(t, x_t, y_t) and for which we don't require the property of uniqueness of - solutions. Third, we study an asymptotic relationship between the solutions of two retarded functional differential equations of Caratheodory type such as: y = A(t)y(t) + B(t)y(t-r) + f(t,y_t) x = A(t)x(t) + B(t)x(t-r) + f(t,x_t) + g(t,x_t) > where A(t) = diag[a_i(t)]nxn , and B(t) = [b_ij(t)]nxn .