∂z/∂x = ∂f /∂u * ∂u/∂x = 3 fu'∂²z / ∂x∂y = 3 fuu'' * ∂u/∂y + 3 fuv'' * ∂v/∂y= 3 fuu'' * 2 + 3 fuv'' * 2y= 6 fuu'' + 6...