Prove Theorem 11.10: If $\mathbf{x}=\mathbf{x}(u, v)$ is a patch on a surface of class $=2$ such that $E=E(u), F=0$ and $G=G(u)$, then
(i) the $u$-parameter curves $v=$ constant are geodesics,
(ii) the $v$-parameter curve $u=u_0$ is a geodesic iff $G_u\left(u_0\right)=0$,
(iii) a curve $\mathbf{x}=\mathbf{x}(u, v(u))$ is a geodesic iff $v= \pm \int \frac{C \sqrt{E}}{\sqrt{G} \sqrt{G-C^2}} d u, C=$ constant.