Triangular knowledge concept

1, triangle: A figure composed of three line segments that are not on the same line end to end is called a triangle.

2. Trilateral relationship: the sum of any two sides of a triangle is greater than the third side, and the difference between any two sides is less than the third side.

3. Height: Draw a vertical line from the vertex of the triangle to the line where the opposite side is located, and the line segment between the vertex and the vertical foot is called the height of the triangle.

4. midline: in a triangle, the line segment connecting the vertex and its relative midpoint is called the midline of the triangle.

5. Angular bisector: The bisector of the inner angle of a triangle intersects the opposite side of this angle, and the line segment between the vertex and the intersection of this angle is called the angular bisector of the triangle.

6. Stability of triangle: The shape of triangle is fixed, and this property of triangle is called stability of triangle.

7. Polygon: On the plane, a figure composed of some line segments connected end to end is called polygon.

8. Interior Angle of Polygon: The angle formed by two adjacent sides of a polygon is called its interior angle.

9. Exterior angle of polygon: The angle formed by the extension line of one side of polygon and its adjacent side is called the exterior angle of polygon.

10, diagonal of polygon: the line segment connecting two non-adjacent vertices of polygon is called diagonal of polygon.

1 1, regular polygon: a polygon with equal angles and sides in a plane is called a regular polygon.

12, plane mosaic: a part of the plane is completely covered by some non-overlapping polygons, which is called covering the plane with polygons.

13, formula and properties:

(1) Sum of internal angles of triangle: The sum of internal angles of triangle is 180.

(2) the nature of the triangle exterior angle:

Property 1: One outer angle of a triangle is equal to the sum of two inner angles that are not adjacent to it.

Property 2: The outer angle of a triangle is larger than any inner angle that is not adjacent to it.

(3) The formula of the sum of polygon internal angles: Is the sum of polygon internal angles equal to? 180

(4) Sum of polygon external angles: the sum of polygon external angles is 360.

(5) Number of diagonal lines of a polygon: ① Starting from a vertex of a polygon, a diagonal line can be drawn to divide the polygon into triangles. ② The polygon * * * has a diagonal line.