elliptic integral
C = 2 π ( ∑ i = 1 n a 2 s i n α 2 i + b 2 c o s α 2 i n ) {\displaystyle C=2\pi ({\frac {\sum _{i=1}^{n}{\sqrt {a^{2}sin_{\alpha }^{2}\,\!i+b^{2}cos_{\alpha }^{2}\,\!i}}}{n}})}
sin,cos-in degrees for a = b we get the circumference of a circle
