I am currently trying to solve a problem but have no idea how to go about it. The question reads:
Show that a Compact Surface with Genus $1$ has points where the Gaussian Curvature is positive, negative and points where it vanishes.
Now, by an application of Gauss Bonnet for Compact Surfaces, I got: $$\int_{S}Kd\sigma = 2\pi\cdot\chi(S)$$ Because the Genus of the Surface is given by: $$G=\frac{2-\chi(S)}{2}$$ Obviously the Euler Characteristic of this Surface is $0$. But then the Integral of the Gaussian Curvature over $S$ gives $0$. I don't know how I can conclude anything from that, or if it even means anything in the first place. If someone is willing to help me out it would be greatly appreciated.
EDIT
The question was wrong (with $g=0$). A round sphere gives you a counterexample. Try proving the statement for $g=1$, however. :) [You will still need to show that there is some point where the Gaussian curvature is positive. Then the rest will follow immediately.]