Let $(g_{ij})$ be the fundamental tensor of the Finsler metric $F$, that is $g_{ij}(x,y) := \frac{1}{2}\frac{\partial^{2}F^{2}}{\partial y^{i}\partial y^{j}}$.
$$D\Big(\log \big(\sqrt{\det (g_{ij})}\big) \Big)=\frac{1}{2}g^{ij}Dg_{ij}.$$
My Question: Why $D(\det(g_{ij})) = D(g_{ij})$?