Dear Kitonum,

Exp (t) in your formula for A'(t), is not a function of A (t). Actually I want to form an ODE for A (t) and its first derivative A'(t), without presence of variable "t"or any function of "t". In other words, a function witch satisfies A' (t)=f (A(t)).

Tnx.

Hi Mehdi,

thanks for your answer.

My question rose when I wanted to express the derivatives of a function in terms of the function itself. lets assume A(t) = ln(exp(t)+a+sqrt(exp(t)-a+b)). then if A'(t) can be expressed as a function of A(t), what that function will be?