Etude de l'equation
      x"+ x = 0 , x(0) =1, x'(0)=0

            Makhlouf Amar
universite de Annaba, institut de mathematiques
       BP 12, EL Hadjar, Annaba, Algerie

We consider the non linear differential equation:
x"+x = 0, x(0) =1, x'(0)=0 (1), where the variable t is complex. The
solution of (1) is multiperiodic: we calculate the periods of this
solutions. By using two relations which we independent periods. We have
two real independent periods and two imaginary independent periods.

mots cle: periode, solution multiperiodique, lacet.