Sub ZBRAC(X1, X2, SUCCES)
    FACTOR = 1.6
    NTRY = 50
    If X1 = X2 Then Print "you have to guess an initial range"
    F1 = FUN(X1)
    F2 = FUN(X2)
    SUCCES = True
    For J = 1 To NTRY
        If F1 * F2 < 0 Then Exit Sub
        If Abs(F1) < Abs(F2) Then
            X1 = X1 + FACTOR * (X1 - X2)
            F1 = FUN(X1)
        Else
            X2 = X2 + FACTOR * (X2 - X1)
            F2 = FUN(X2)
        End If
    Next J
    SUCCES = False
End Sub