# calculus and analysis – Multiple derivative of unknown function from time-dependent parameter

I am working with the unknown function $$j$$, which depends on the parameter $$phi(t)$$, i.e.

$$J=f_1(phi(t))+f_2(phi(t))$$.

I find derivative $$frac{d}{dt}(frac{dJ}{dtheta(t)})=?$$ in implicit form and get formula:

``````J = f1((Theta), t) + f2((Theta), t)
D(D(J, (Theta)), t)
``````

Reason: General derivative of $$J$$ function can be much more complex, and the implicit representation allows it to be represented as a sum of simpler components. These are the components I’m going to explore.

Problem: How do I turn this formula into a programming-friendly one in Mathematica?