In order to follow my book on General Relativity, I need to prove the above relation, where $g_{ab}$ is some general metric, $\partial_c$ denotes the partial derivative with respect to $x^c$, $\partial_c=\frac{\partial}{\partial x^c}$ and, as it's said on the title, $g$ is the determinant of the metric matrix.
On the book it's said (and seems like it's useful for the proof) that the cofactor of the element $g_{ab}$ in this determinant is $gg_{ab}$, but I can't see why this would be true...
Any help would be much appreciated!
