1. A circle is a conic curve with only one side. In a plane, a closed curve formed by a moving point rotating around a certain point with a certain length is called a circle. A circle has countless axes of symmetry.

2. A triangle has three sides, which are divided into isosceles triangle, equilateral triangle and arbitrary triangle. According to angle, it is divided into acute triangle, right triangle and obtuse triangle.

3. Square is a special parallelogram. That is, a group of parallelograms with equal adjacent sides and a right angle is called a square, also known as a regular quadrilateral. It has all the characteristics of rectangle and diamond.

Extended data:

Knowledge points induction of graphic classification;

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. According to different standards, the known graphics are classified.

1, classified by plane graphics and three-dimensional graphics.

2, according to whether the plane figure is composed of line segments to classify.

3. According to the number of edges of the graph. Through self-help classification, we can re-recognize the graphics and understand their characteristics.