The length of a closed graph is called perimeter, and the length of a graph is called perimeter. Therefore, the perimeter is equal to the sum of all the edges of the graph. Generally, it is represented by the letter C. If it is a triangle with the same area, the perimeter of an equilateral triangle is the shortest. If it is a quadrilateral with the same area, the perimeter of the square is the shortest; If pentagons with the same area are used, the perimeter of regular pentagons is the shortest; If you use any polygon with the same area, the circumference of a regular circle is the shortest. Perimeter can only be used on two-dimensional figures (planes and surfaces), and three-dimensional figures (solids) such as cylinders, cones and spheres can't express their boundary size by perimeter, but by total surface area.

With the development of society, various tools have emerged to meet the needs of people's real life and work. The perimeter and area measuring instrument is no exception. Its purpose is to help people measure the perimeter and area of any plane figure conveniently, quickly and accurately. The principle of perimeter and area measuring instrument is to convert one curve into another curve according to a given law by using the converter principle.

The perimeter of a polygon is also equal to the sum of all sides of the graph, the perimeter of a circle =πd=2πr(d is the diameter, R is the radius, π), and the perimeter of a sector =2R+nπR÷ 180_(n= central angle) =2R+kR(k= radian).

Formula for finding perimeter

1, the perimeter of the rectangle = (length+width) ×2, and C=(a+b)×2.

2. The circumference of a square = side length ×4, and C=4a.

3. The area of a rectangle = length × width, and S=ab.

4. Square area = side length × side length, S = a * a ..

5. The area of triangle = base × height ÷2, and S=ah÷2.

6. The area of parallelogram = base × height, and S=ah.

7. Trapezoidal area = (upper bottom+lower bottom) × height ÷2, s = (a+b) h ÷ 2.

8. Diameter = radius× 2d = 2r, radius = diameter ÷2, r=d÷2.

9. The circumference of a circle = π× diameter = π× radius× 2, and c = π d = 2π r. ..

10, area of circle = pi × radius, _ = π r.