How to determine the distance between the foci of an ellipse?

[wraith pond]

For example, the length of the major axis is 20 meters while the minor axis is 8 meters. How would I go about this and solve for the distance of the foci?

[still rapids]

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[weary ember]

it's just e*major ax

e is the eccentricity

[wraith pond]

eccentricity is distance of focus from center/major axis right?

or c/a

[weary ember]

it's the the ratio of distance from directrix and focus

look up the order

dir/focus or focus/dir i forgor

[noble jasper]

36.3 approx distance between them