1, squared
A quadrilateral with four equal sides and four right angles is a square. The two groups of squares have parallel opposite sides and equal four sides; All four angles are 90 degrees; Diagonal lines are perpendicular, bisected and equal to each other, and each diagonal line bisects a set of diagonal lines.
Step 2: Triangle
Ordinary triangles are divided into ordinary triangles (three sides are unequal) and isosceles triangles (isosceles triangles with unequal waist and bottom and isosceles triangles with equal waist and bottom, that is, equilateral triangles); According to the angle, there are right triangle, acute triangle and obtuse triangle, among which acute triangle and obtuse triangle are collectively called oblique triangle.
3. Circle
A circle is a geometric figure. By definition, compasses are usually used to draw circles. The diameter and radius length of the inner circle of the same circle are always the same, and the circle has countless radii and diameters. A circle is a figure with axial symmetry and central symmetry.
The axis of symmetry is the straight line where the diameter lies. At the same time, the circle is a "positive infinite polygon" and "infinity" is just a concept. The more sides a polygon has, the closer its shape, perimeter and area are to a circle. So there is no real circle in the world, and the circle is actually just a conceptual figure.
4. Cubes
Cubes, also called cubes, are regular polyhedrons composed of six square faces, so they are also called regular hexahedrons. It has 12 edges and 8 vertices. Cube is a special kind of cuboid.
5. Prism
Prism is a common three-dimensional polyhedron in geometry, which refers to a closed geometry that two parallel planes are vertically cut by three or more planes.
If the number of planes used to cut parallel planes is n, then this prism is called an n prism. For example, a triangular prism is a closed geometric figure cut vertically from two parallel planes and three planes.