本文讨论了指向定点及垂直指向定直线或定平面的力的作功问题，并给出了一个统一的计算公式。

This paper discusses the problems of doing work by the forces pointing at the definite point or vertically at the definite line or plane. And a calculating formula is given.

本文讨论了三维空间中到两定直线的距离之比为常数的点的轨迹。

This paper discusses the loci of moving points with constant ratios of distances from two fixed lines.

利用二次曲面的不变量判定到一定点和一定平面(定直线)的距离之比为常数的空间点的轨迹。

Make use of constant measure of second order curved face, and judge the space figure that arrive the fixed point and the fixed flat surface (fixed straight line) distance's ratio is a constant.

光波以直线形式传播。

Sound and light propagate in this medium.

定窑还有北定、南定之分。

Ding also north and south will be divided.