判断线段是否位于第一象限；计算线段长度；判断两条线段是否相交；计算点到线段（直线）的距离；用户交互给出线段和点的坐标-Determine whether the line in the first quadrant　calculated length of the line　to determine whether the intersection of two segments　calculation points to the line (straight line) distance　user interaction is given the coordinates of line segments and points