1, definition, proportional line segment refers to the proportional relationship between two line segments, and the proportional line segment is called proportional line segment.
2. The theorem of proportional barycenter means that on a straight line of a triangle, the proportional barycenter of three line segments, that is, their equal points, are all located on the "barycenter" of the straight line with a fixed point on it.
3. The Trinity Theorem means that when three parallel lines divide any straight line into several line segments, the ratio of the line segments on both sides of one pair of diagonal lines is equal to the ratio of the line segments on both sides of the other pair of diagonal lines.
The basic nature of proportional line segment is a basic and important concept in mathematics education. It is not only explained in junior high school mathematics, but also applied in senior high school mathematics.