A favorite of mine is the Gauss-Bonnet theorem which relates the Euler characteristic of a surface (i.e. its topology) to its Gaussian curvature (its differenti

A favorite of mine is the Gauss-Bonnet theorem which relates the Euler characteristic of a surface (i.e. its topology) to its Gaussian curvature (its differential geometry). https://en.wikipedia.org/wiki/Gauss–Bonnet_theorem https://en.wikipedia.org/wiki/Gauss–Bonnet_theorem