1, geometry

Various graphics abstracted from objects, including three-dimensional graphics and plane graphics.

Three-dimensional figures: Some geometric figures are not all on the same plane, but three-dimensional figures.

Plane figure: All parts of some geometric figures are on the same plane. They are plane figures.

2. Points, lines, surfaces and bodies

Synthesis of (1) Geometry

Point: The intersection of straight lines is the point, which is the most basic figure in geometry.

Line: The intersection line between faces is a line, which can be divided into straight lines and curves.

Face: Surrounding the body is a face, which is divided into plane and curved surface.

Volume: Geometry is also called volume for short.

(2) Points move into lines, lines move into planes, and planes move into adults.

3, the three-dimensional graphics in life

Cylinder (the side of the cylinder is curved and the bottom is round)

pillar; mainstay

Spherical prisms of three-dimensional figures in life: triangular prism, quadrangular prism (cuboid, cube), pentagonal prism, …

The side of a prism is composed of several small rectangles, and the bottom is polygonal. )

(name) Conical cone (the side of a cone is curved and the bottom is round)

Pyramid (the side of the pyramid is composed of several triangles and the bottom is polygonal)

4, prism and related concepts:

Edge: In a prism, any intersection of two adjacent faces is called an edge.

Side: The intersection of two adjacent sides is called a side.

N prism has two bottom faces, n side faces and ***(n+2) faces; 3n sides and n sides; 2n vertices.

5. Cubic plane development diagram: 1 1 species.

Cut a cube: cut a cube with a plane. The cutting surface can be triangular, quadrilateral, pentagonal or hexagonal.

Possibility: acute triangle, equilateral triangle, isosceles triangle, square, rectangle, non-right parallelogram, non-isosceles trapezoid, isosceles trapezoid,

Pentagon, hexagon, regular hexagon

Impossible: obtuse triangle, right triangle, right trapezoid, regular pentagon, heptagon or more polygons.

8 through views

Three views of an object refer to the front view, the top view and the left view.

Front view: The view seen from the front is called the front view.

Left view: The picture seen from the left is called the left view.

Top view: The view from above is called top view.

Note: The three views obtained from the stereogram are unique, but the stereogram recovered from the three views is not necessarily unique.

Polygon: a closed plane figure composed of line segments that are not on the same line, called polygon.

1. Starting from the same vertex of the n- polygon, the N- polygon can be divided into (n-2) triangles by connecting this vertex with other vertices respectively.

2. If f represents the number of faces of a regular polyhedron, e represents the number of edges and v represents the number of vertices, then f+v-e=2.

Arc: The part between point A and point B on a circle is called an arc.

Sector: A figure consisting of an arc and two radii passing through the end of the arc is called a sector.