1. The problem statement, all variables and given/known data Taking k and ω to be constant, ∂z/∂θ and ∂z/∂ф in terms of x and t for the following function z = cos(kx-ωt), where θ=t2-x and ф = x2+t. 2. Relevant equations 3. The attempt at a solution I'm finding this difficult as t and x are not stated explicitly. I know how to do the chain rule with partial differentiation.