设函数在点处存在关于和的一阶偏导数，则极限的值为.https://img-ph-mirror.nosdn.127.net/AzSolBHpAcwrMwJeuCZ3qw==/6608821346933715540.pnghttps://img-ph-mirror.nosdn.127.net/riflWFLWLx67TbwPlzd9tA==/6608437617375621610.pnghttps://img-ph-mirror.nosdn.127.net/dyIPWyFt4Slg58f2hJhSgA==/6599324865005947430.pnghttps://img-ph-mirror.nosdn.127.net/UdiS2LasHHPU1rvP0W8m0g==/6599309471843212852.pnghttps://img-ph-mirror.nosdn.127.net/9E39I3VJ73DxsgLGL8JhGg==/6608841138143042768.png