hi! i have:

deq := {diff(a(t,y),y,y)/a(t,y) + (diff(a(t,y),y)/a(t,y))^2 - ((diff(a(t,y),t))/(n(t,y)*a(t,y)))^2, (diff(a(t,y),y)/a(t,y))*((diff(a(t,y),y)/a(t,y))+(diff(n(t,y),y)/n(t,y))) - (1/n(t,y)^2)*((diff(a(t,y),t,t)/a(t,y))+((diff(a(t,y),t)/a(t,y))*((diff(a(t,y),t)/a(t,y))-(diff(n(t,y),t)/n(t,y)))))};

i've solved it by using a package: "Formal series solutions to non-linear DE (ODE or PDE) or systems of them
(Cauchy problem)". then, i defined three new parameters: