中文摘要：

在这份报纸，秒顺序的极值方向性的衍生物，即一阶的衍生物的坡度被讨论。在三个 nonparallel 方向给秒顺序方向性的衍生物，或给秒顺序方向性的衍生物并且在二个 nonparallel 方向混合方向性的衍生物，为秒顺序的极值的公式方向性的衍生物被导出，并且相应于最大值和最小的方向对对方垂直。

英文摘要：

In this paper, the extremum of second-order directional derivatives, i.e. the gradient of first-order derivatives is discussed. Given second-order directional derivatives in three nonparallel directions, or given second-order directional derivatives and mixed directional derivatives in two nonparallel directions, the formulae for the extremum of second-order directional derivatives are derived, and the directions corresponding to maximum and minimum are perpendicular to each other.