1. Definition of the midline of a triangle: a line segment connecting a vertex of a triangle with the midpoint of the opposite side;

2. The center line of the triangle can divide the triangle into two parts with equal area;

3. The three midlines of a triangle must intersect at one point, and the intersection point is the center of gravity of the triangle;

4. Gravity center theorem: the distance from the gravity center of a triangle to the vertex is equal to twice the distance from the midpoint of the opposite side;

5. The three median lines of a triangle can divide the triangle into six parts with equal area;

6. To solve the problem of triangle midline, the commonly used auxiliary lines are double-length midline, congruent triangles or parallelogram;

7. When two midlines of a triangle appear at the same time, it is often necessary to consider the midline of the triangle: the midline of the triangle is parallel and equal to half of the third side;

8. The median line on the hypotenuse of a right triangle is equal to half of the hypotenuse;

9. If the midline of one side of a triangle is equal to half of this side, then this triangle is a right triangle;

10. The bisector of the top angle, the height on the bottom edge and the midline on the bottom edge of the equilateral triangle coincide;

1 1. If AD is the center line of △ABC, then vector AB+ vector AC=2* vector AD.