αz/αx=ln(xy)+x×1/(xy)×y=1+ln(xy)<br>αz/αy=x×1/(xy)×x=x/y<br>α^2z/αx^2=1/(xy)×y=1/x<br>α^2z/αxαy=1/(xy)×x=1/y<br>α^2z/αy^2=-x/y^2