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The second question:

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The third question:

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This part of the extended data mainly examines the knowledge points of line segments:

A finite part between two points on a straight line (including both endpoints)? , different from straight lines and rays. The general term in technical drawing refers to a continuous or discontinuous drawing line composed of one or more different line elements, such as a solid line segment or a double-point long line segment composed of "long stroke, short interval, point, short interval, point and short interval".

Connect two points with a ruler and you get a line segment. The length of a line segment is the distance between these two points. The length of the line segment connecting two points is called the distance between these two points.

Line segments are represented by letters A and B or lowercase letters representing their two endpoints. Sometimes these letters also represent the length of the line segment, which is recorded as line segment AB or line segment BA, line segment A .. where A and B represent the two endpoints of the line segment.