1, the properties of the external angle of triangle:
(1) Vertex is the vertex of a triangle, one side of the triangle is the extension of one side of the triangle, and the other side is the extension of one side of the triangle.
(2) The outer angle of a triangle is equal to the sum of two non-adjacent inner angles.
(3) The outer angle of a triangle is larger than any inner angle that is not adjacent to it.
(4) The sum of the external angles of the triangle is 360, the internal angle of the triangle is the included angle of two line segments, and the sum of the internal angles of the triangle is180; One outer angle of a triangle is equal to the sum of the other two inner angles; One outer angle of a triangle is larger than the other two inner angles.
2, the relationship between the triangle outside Angle and inside Angle:
The inner angle is the included angle of the side, and the outer angle is the included angle between the adjacent side and the extension line of one side; The inner angle is the angle enclosed by the adjacent edges inside the closed figure, and the outer angle is the angle formed by the outer edge of the closed figure and the extension line of the adjacent edges.
The sum of the external angles of a triangle is 360 degrees, and 360 degrees can be divided into at least four right angles, that is, the external angles have at least four right angles, because the external angles are complementary to the adjacent internal angles.
Application of triangle:
1, architectural design:
Architects need to use triangles when designing buildings to ensure the stability and structural strength of buildings. For example, triangular supports can be used to support the structure of high-rise buildings.
2, map drawing:
The triangle on the map can be used to measure the distance and determine the position. Triangulation is a measurement method based on the principle of triangle, which can be used to measure the distance and angle on the earth.
3. Art design:
Triangles are often used in artistic design. They can be used to create various shapes and patterns. For example, a big triangle can be divided into many small triangles to make complex patterns.
4. Biology:
In biology, triangles can be used to describe molecular structures and chemical bonds. Some molecules, such as protein and DNA, have a triangular structure.
5. Toy manufacturing: triangles can be used to make various toys, such as puzzles and building blocks. These toys can help children learn math and geometry.