Rectangle: Two groups of opposite sides are equal in length. They are parallel and unstable. It is a special parallelogram with two symmetrical axes. Square: The four sides are completely equal and unstable, which is a special rectangle. Parallelogram, unstable, without symmetry axis. Triangle: isosceles triangle and equilateral triangle 1. An isosceles triangle has two equal sides and 1 symmetry axis. 2. The three sides of an equilateral triangle are completely equal and have three symmetry axes. Triangle is divided into acute triangle, right triangle and obtuse triangle: 1. All three angles of an acute triangle are acute angles. 2. Right triangle, one angle is right angle and the other two angles are acute angles. 3. One angle is obtuse and two angles are acute. Circle: There are countless symmetry axes, countless diameters and countless radii. The distance from the center of the circle to any point on the circle is equal everywhere, and the straight line with the diameter is its symmetry axis! Hey, hey, ............................................................................................................................................................................ picked me!