1, triangle

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.

A closed figure composed of three line segments that are not on the same straight line is called a triangle. A figure surrounded by three straight lines on a plane or three arcs on a sphere is called a plane triangle; A figure surrounded by three arcs is called a spherical triangle, also known as a triangle.

2. Square.

A square is a quadrilateral with four congruent 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. A group of parallelograms with equal adjacent sides and a right angle is called a square. A quadrilateral with four equal sides and four right angles is a square.

Two groups of opposite sides of the square are parallel to the beam ring respectively, and the four sides are equal; 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. A group of parallelograms with equal adjacent sides and a right angle is called a square. A group of rectangles with equal adjacent sides is called a square, and a diamond with an angle of 90 is called a square. Square is a special form of rectangle and diamond.

3. Rectangular.

Rectangle, a mathematical term, is a parallelogram with right angles called rectangle. It is also defined as a parallelogram with four right angles, and a square is both a rectangle and a diamond. The essence of a rectangle is: two diagonal lines are equal; Two diagonal lines are equally divided; Two groups of opposite sides are parallel respectively; The two groups of opposite sides are equal respectively; All four corners are right angles; There are two symmetrical axes (there are four squares); It is unstable (easily deformed).

The square of the diagonal length of a rectangle is the sum of the squares of both sides; The quadrangle obtained by connecting the midpoints of the sides of the rectangle in turn is a diamond-shaped orange withered. According to custom, the long side of a rectangle is called long and the short side is called wide. The same direction as the horizontal plane is called long, and vice versa. The length and width of a rectangle are relative, so we can't absolutely say "longer than wider".