The first chapter is a rich graphic world.
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 point where straight lines intersect 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 the face, which is divided into plane and curved surface.
Volume: Geometry is also called volume for short.
(2) inching into a line, the line moves into a plane, and the plane moves into an adult. xK b 1。 chief operating officer
3, common geometry and its characteristics
Cuboid: It has 8 vertices, 12 sides and 6 faces. All faces are rectangles (squares are special rectangles) and cubes are special cuboids.
Prism: the upper and lower sides are called the bottom of the prism, the other sides are called the side faces, and the cuboid is a quadrangular prism.
Pyramid: One face is a polygon and the other faces are triangles with a common vertex.
Cylinder: It has two bottom surfaces and one side surface (curved surface), and the two bottom surfaces are circles with the same radius. The surface development diagram of a cylinder is formed by connecting two identical circles and a rectangle.
Cone: It has a bottom surface and a side surface (curved surface). The side development diagram is fan-shaped and the bottom surface is round.
Sphere: Geometry surrounded by a surface (surface).
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.
6. Cut a cube:
(1) Cut a cube with a plane, and the cutting surface can be triangle, quadrilateral, pentagon or hexagon.
Note: ① A cube has only six faces, so the cross section has at most six sides, that is, the figure with the largest number of sides is hexagonal. ② The cross sections of cuboids and prisms are similar to those of cubes.
(2) When the cylinder is cut by plane, the following situations may occur.
(3) Two kinds of sections, circular and triangular, can be cut out by plane cutting cone (there are other sections that can't be learned in junior high school)
(4) When cutting a sphere with a plane, there can only be one cross-sectional shape-circle. W W W X K B 1 C O M
(5) Key points to remember:
Geometric cross-sectional shape
Cubes are triangular, square, rectangular, trapezoidal, pentagonal and hexagonal.
Cylindrical, rectangular, (square), ...
Cone, circle, triangle, ...
Spherical circle