What is an inner corner? For example, the 60-degree angle of an equilateral triangle is its inner angle, and the 120-degree angle outside the graph is its outer angle. The formula for the sum of internal angles of any N-polygon is θ = 180 (n-2). Where θ is the sum of the internal angles of an n-polygon, and n is the number of sides of a polygon. A polygon can be divided into (n-2) triangles by connecting one vertex with other vertices, and the sum of the internal angles of each triangle is 180. Therefore, the formula for the sum of internal angles of any N-polygon is: θ = (n-2) 180, n=3, 4, 5, ...
The formula for calculating the sum of external angles is usually internal angle+external angle = 180 degrees, so the sum obtained by adding each external angle separately becomes the sum of external angles of polygons. The sum of the inner and outer angles of the N polygon is n× 180, and the sum of the inner angles of the N polygon is (n-2 )× 180, so the sum of the outer angles of the N polygon is 360. This means that the outer angle of a polygon has nothing to do with the number of sides. When solving the problem about the sum of the inner angle and the outer angle of a polygon, we usually use the formula series equation to solve the problem. Moreover, the outer angle of a triangle is equal to the sum of two non-adjacent inner angles.
The nature of complementary angle: the complementary angle of the same angle or equal angle is equal.
It includes the following two aspects:
1. The complementary angles of the same angle are equal. That is, if ∠ A+∠C=∠B = 180, ∠ A+∠ C = 180, ∠C=∠B.
2. The complementary angles of equal angles are equal. Namely: ∠ A+∠ B = 180, ∠ D+∠ C = 180, ∠A=∠D, then ∠C=∠B,.