The length integral of the edge around a finite area is called the perimeter, which is the length of a graph. The perimeter of a polygon is also equal to the sum of all sides of the graph, the perimeter of a circle = π d = 2π r (D is the diameter, R is the radius, π), and the perimeter of a sector = 2r+nπ r ÷ 180 (n = central angle) = 2r+kr (k = radian).

Content standard

"Understanding of perimeter" is the learning content of the third grade in the first phase of compulsory education mathematics (Volume I), and it is also the learning content of "Understanding of perimeter" in the curriculum standard.

In fact, it includes three levels: first, let students know the concept of perimeter and experience it in real life; Secondly, let students master the method and process of measuring circumference; Finally, experience and feel the application of mathematics in life.