1. The problem statement, all variables and given/known data Rewrite this in terms of f, f, ∂f/∂x, and x: ∂f(x,y)/∂(%Δx) = ∂f(x,y)/∂(d log(x) ) 2. Relevant equations ∂(%Δf(x,y))/∂(%Δx) = ∂logf(x,y)/∂log(x)= ∂f(x,y)/∂x*x/f(x,y). ∂f(x,y)/∂log(x)=x∂f(x,y)/∂x 3. The attempt at a solution I found that (%Δx) can be written as the differential of log(x): ∂f(x,y)/∂(%Δx) = ∂f(x,y)/∂(d log(x) ). But the partial of derivative of differential of the variable throws me off. It seems like the valid problems that people may have in real world: how much the level of function changes if you increase 1% of the variable, but I can't find anything on it.