Line segment
A line segment is a part of a straight line with dots on both ends. In other words, of all kinds of lines in mathematics, since there are only end points on both sides of a line, it is simple and efficient to express a certain line segment mathematically by using the points on both ends. Therefore, a line segment with both ends of points A and B is defined as segment AB. In addition, since the line segment has both ends, there is a unique feature that can measure the length, unlike the straight line and the half line having infinite length. Since the length of a line is limited based on two points, the outer portion of the line is also defined. That is, the portion existing on the line AB but not on the line AB is referred to as an extension of the line AB. These features of the line segment may lead to several formulas. When a point on line segment AB is called P, P divides line segment AB, and P at this time is called the end point of AB. Also, when a point on the extension line of line segment AB is Q, Q excretes line segment AB, where Q is the outline point of segment AB.