lim[2-√(xy+4)]/xy
=lim[2-√(xy+4)][2+√(xy+4)]/{xy[2+√(xy+4)]}
=lim(x-->0,y---->0)(-xy)/[xy[2+√(xy+4)]]
=-lim(x-->0,y---->0)1/[2+√(xy+4)]
=-1/4谢谢，你是学生吗？