Ellipse

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Ellipse Formulas

Ellipse equation : $x^2 / a^2 + y^2 / b^2 = 1$

	a > b	a < b
Semimajor axis	a	b
Semiminor axis	b	a
Major axis	2a	2b
Minor axis	2b	2a
Focal axis	x-axis	y-axis
Non focal axis	y-axis	x-axis
Center - Foci distance	$c = sqrt(a^2-b^2)$	$c = sqrt(b^2-a^2)$
Focal distance (FF')	2c	2c
Center - Vertex distance	a	b
Center - Co-vertex distance	b	a
Eccentricity	$e = c/a$	$e = c/b$
Center - Directrix distance	$d = a^2/c$	$d = b^2/c$
Area	$piab$	$piab$
Perimeter (Ramanujan approximation)	$pi(3(a+b)$ - $sqrt(10ab+3*(a^2+b^2)))$