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Hello I am stucked on this problem: let $\mathrm{char}k=0$ and let $X=\mathcal{V}(zy^2-x^2(x+z))\subset\mathbb{P}^2$ in homogeneous coordinates $x,y,z$. Let $o=[0:0:1]$, $r=[-1:0:1]$ and $s=[0:1:0]$ points of $X$ and let $U_1=X-\{o\}$ and $U_2=X-\{r,s\}$. I want to show that the Cartier Divisor $D ...