The length |AB| of the line segment AB, and the length |AB→| of the directed line segment, is equal to the distance between A and B. It is equal to zero when A and B coincide and is otherwise always positive.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。