Some knowledge points in the first volume of junior high school mathematics textbook catalogue (1) geometry
All kinds of figures abstracted from objects are collectively called geometric figures. Geometric graphics are divided into three-dimensional graphics and plane graphics.
(2) Three-dimensional graphics
A three-dimensional figure is a geometric figure whose parts are not in the same plane, and it is surrounded by one or more surfaces that can exist in real life. Points become lines, lines become faces, and faces become bodies.
Classification: cylinder, cone, rotating body, sectional body, etc.
(3) Plane graphics
Plane figure is a kind of geometric figure, which means that all points are on the same plane, such as straight line, triangle and parallelogram. Are basic plane figures.
Classification: circle, polygon, bow, multi-arc.
(4) Points, lines, surfaces and bodies
Point: Point is the simplest shape and the most basic component of geometric figure. A point is a figure with only position but no size in space.
Line: A line is a figure composed of countless points.
Face: the trajectory from two points in space to a point with the same distance.
Volume: A polyhedron is a solid surrounded by four or more polygons.
(5) Lines, rays and line segments
Straight line: A straight line consists of countless points. There is no end point, extending to both ends indefinitely, and the length cannot be measured. A straight line is an axisymmetric figure.
Ray: refers to a straight line formed by the infinite extension of one end of a line segment. The light has only one endpoint, so the length cannot be measured.
Line segment: refers to the limited part (including two endpoints) between two points on a straight line, which is different from straight lines and rays.
(6) Angle: In geometry, an angle is a geometric object composed of two rays with a common endpoint. These two rays are called the edges of an angle, and their common endpoint is called the vertex of the angle.
(7) Complementary angle: If the sum of the two angles is 90, the two angles are complementary to each other, and the complementary angles of equal angles are equal.
(8) Complementary angle: If the sum of two angles is 180, then the two angles are complementary angles, and the complementary angles of equal angles are equal.