quality:corruption
Eccentricity

The eccentricity can be expressed as: e = c a = 1 − (b a) 2, {\displaystyle e={\frac {c}{a}}={\sqrt {1-\left({\frac {b}{a}}\right)^{2}}},}

assuming a > b. {\displaystyle a>b.} An ellipse with equal axes (a = b {\displaystyle a=b}) has zero eccentricity, and is a circle.