A square is a quadrilateral with four equal sides and four right angles.

Its two groups of opposite sides are parallel, the four sides are equal, and the 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, which is a special form of rectangle and diamond.

Triangle is a closed figure composed of three line segments in the same plane but not on the same straight line, and it is the basic figure of geometric pattern.

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.