1, perimeter of triangle (general triangle, Helen formula) L = a+b+c(a, b and c are the lengths of three sides of triangle)

2. The circumference of the rectangle L = 2 (a+b) (A and B are the lengths of the adjacent sides of the rectangle).

3. Square perimeter L = 4a

4. trapezoid perimeter L = a+b+c+d(a: upper bottom, b: lower bottom, the length of c and d, the same below).

5. Perimeter L = 2πr(π:π, r: radius of circle)

6. The accurate calculation of ellipse circumference (L) requires the summation of integral or infinite series, for example.

(0-pi/2) integral of l = 4a * sqrt (1-e sin t), where a is the major axis of the ellipse and e is eccentricity.

7. If the radius is r and the central angle of the sector is n, the perimeter of the sector is:

C=2R+nπR÷ 180

8. The circumference of a semicircle = π r+2r = π d/2+d.

Just remember these. . . The perimeter is the length of a week. As long as you know the side length of the figure, add it up.