\[xrdis=dlx(k_{1}r^{2}\ +\ k_{2}r^{4}\ +\ k_{3}r^{6})\] \[yrdis=dly(k_{1}r^{2}\ +\ k_{2}r^{4}\ +\ k_{3}r^{6})\] \[xtdis=2p_{1}dlx\ dly\ +p_{2}(r^{2}\ +\ 2dlx\text{\ dlx}^{2})\] \[ytdis=p_{1}\left(r^{2}\ +\ 2\text{dly}^{2}\right)+2p_{2}\text{dlx\ dly}\]
(3)