We now have & a system of four differential equations (3', 4', 5 and 6) and four dot variables (k, B, x and I) which can be solved.
& (3' ) U '' ( x ) ⋅ x = U '⋅( ρ − i ) ∂f & & ( 4' ) U ' ( x ) ⋅ C' '( I ) ⋅ I + U ' ' ( x ) ⋅ C'( I ) ⋅ x = U '⋅( x ) ⋅ C'( I ) ⋅ (δ + ρ ) − U '( x ) P ∂k & On peut remanier les équations 3' et 4' de manière à ce que x et I figurent dans le membre de & gauche de l’équation.