As we all know, a quadrilateral can be divided into two triangles, a Pentagon can be divided into three triangles, a hexagon can be divided into four triangles, and a heptagon can be divided into five triangles. From this, it is concluded that an N-polygon can be divided into (N-2) triangles after passing through one of its vertices.

And we know that the sum of the internal angles of triangles is 180 degrees, quadrilateral is 360 degrees, and pentagon is 540 degrees, so the sum of the internal angles of polygons is (N-2) times 180 degrees, and heptagon is 900 degrees.

In geometry, a heptagon refers to a polygon with seven sides and seven vertices, and the sum of its internal angles is 900 degrees. There are many kinds of heptagons, among which regular heptagons are the most symmetrical. Other heptagons can be divided into convex heptagons and non-convex heptagons according to their angle-like properties, in which convex heptagons represent that all internal angles are less than 180 degrees.

A regular heptagon is a regular polygon consisting of seven equal-length sides and seven equal-size angles. A regular heptagon can't be drawn with an uncalibrated ruler and compasses, but it can be drawn with a calibrated ruler. This painting method is called New Zealand painting.

Triangle is a closed figure composed of three line segments on the same plane but not on the same straight line, which has applications in mathematics and architecture.

Triangles are divided into isosceles triangles and equilateral triangles; There are right triangle, acute triangle and obtuse triangle according to the angle. Triangular stability refers to the stability, firmness and compression resistance of triangles, such as Egyptian pyramids, railway tracks, triangular frames, cranes, Eiffel Tower, etc., which are all built according to triangles.

Knowledge expansion

Octagon is a figure in mathematics, which can be divided into regular octagon and irregular octagon. The sum of the inner angles of an octagon is 1080 degrees, the sum of the outer angles is 360 degrees, and the circumference is equal to the sum of the eight sides.

Octagons are used in many aspects of life, such as building structures, regular octagonal honeycombs and birefringent photonic crystal fibers.