Solvability Of Some Classes Of Fourth Order Delay Differential Equations

In this paper,by using the fixed point theorem of cone tension and cone com-pression and the method of upper and lower solutions,we study the existence of positive solutions for some boundary value problems of nonlinear fourth order delay differential equations.The main results as:In the first section,under nonlinear term satisfies asymptotically linear growth condition,by applying the fixed point theorem of cone tension and cone compression,we research the existence of positive solutions for nonlinear fourth order differential equations boundary value problems with delay(?)where f:[0,1]×[0,+?)?[0,+?)is a continuous function,??0,??[(?)/3,1],?>0 is a constant.In the second section,by applying the method of upper and lower solutions,we study the existence of positive solutions of nonlinear fourth order differential equations boundary value problems with delay(?)where f:[0,1]×[0,+?)?[0,+?)is a continuous function,??[1/2,1),??0 is a constant.In the third section,by applying the fixed point theorem of cone tension and cone compression,we study the existence of positive solutions for nonlinear fourth order differential equations boundary value problems with delay(?)where f:[0,1]×[0,+?)?[0,+?)is continuous,?(t)is continuous and ?(0)=0,?>0 is a constant.