Ellipse
Polar form relative to center

In polar coordinates, with the origin at the center of the ellipse and with the angular coordinate θ {\displaystyle \theta } measured from the major axis, the ellipse's equation is r (θ) = a b (b cos θ) 2 + (a sin θ) 2 = b 1 − (e cos θ) 2 {\displaystyle r(\theta)={\frac {ab}{\sqrt {(b\cos \theta)^{2}+(a\sin \theta)^{2}}}}={\frac {b}{\sqrt {1-(e\cos \theta)^{2}}}}} where e {\displaystyle e} is the eccentricity, not Euler's number.
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