l 1=πqn/arctgn:

(b→a、q=a b、n=((a-b)/a)^2、)

This is derived from the principle of perimeter secant, and its accuracy is average. ?

Second,

L2 =ωθ/45(a-c c/sinθ)。

(b→0，c=√(a^2-b^2)，θ=arccos((a-b)/a)^ 1. 1、)

This is derived from the characteristics of the ellipse composed of two pairs of sectors, and the accuracy is average.

Third,

l3=πq( 1 mn)。

(q = b、m=4/π- 1、n=((a-b)/a)^3.3)

This is derived from the formula of circle, and the accuracy is average.

Fourth,

l4=π√(2a^2 2b^2)( 1 mn)。

(q =b、m=2√2/π- 1、n=((a-b)/a)^2.05、)

This is derived from the basic characteristics of ellipse A = B, and its accuracy is average.

Five,

l3=√(4abπ^2 15(a-b)^2)( 1 Mn)。

(m=4/√ 15- 1 、n=((a-b)/a)^9)。

This is derived from the characteristics of ellipses a = b and b = 0, and the accuracy is good.

The exact calculation of ellipse circumference (L) requires the summation of integral or infinite series. It was first proposed by Bernoulli and developed by Euler. The discussion of this kind of problem leads to a branch of mathematics-elliptic integral: the integral of (0-pi/2) l = 4a * sqrt (1-esint), where a is the long axis of the ellipse, e.

Six,

l4 =πq( 1 3h/( 10 √( 4-3h))( 1 Mn)。

(q=a b、h=((a-b)/(a b))^2

m=22/7π- 1、m=((a-b)/a)^33.697)

This is extracted according to the standard formula of ellipse with high accuracy.