express second order derivative of the composite function h(t) = f(ϕ(t), ψ(t)) in terms of the derivatives of ϕ and ψ and partial derivatives of f

[liubava]

 

[HallsofIvy]

Do you not know the "chain rule"?

 

[liubava]

Do you not know the "chain rule"?

Yes, and I have already solved it but thanks