楕円の面積

\(\normalsize Ellipse\\ (1)\ area:\hspace{85px} S=ab\pi,\hspace{20px} b\le a\\ (2)\ circumference:\\ \hspace{20px} L=4aE(k),\hspace{20px} k=\sqrt{1-({\large\frac{b}{a}})^2}\\ \hspace{20px} E(k):\ 2nd\ complete\ elliptic\ integral\\(3)\ ellipticity:\hspace{40px} c={\large\frac{b}{a}}\\ (4)\ linear\ eccentricity :\ f=\sqrt{a^2-b^2}\\\)