How this calculation works
Find the focal offset and eccentricity of an ellipse.
THE FORMULA
c = √[(a−b)(a+b)], eccentricity = c/aA worked example
Semiaxes 5 and 3 place the foci four units from the centre.
Good to know
The major semiaxis must be at least the minor semiaxis.
Reference: OpenStax Algebra and Trigonometry, Trigonometric Applications (opens in a new tab) ↗
Read the result
Find the focal offset and eccentricity of an ellipse.
The primary result is labeled “Focal distance from centre”. Keep the input definitions in view when comparing this result with another method.
Try a related calculation
The major semiaxis must be at least the minor semiaxis.
For a related exercise, try the circle calculator.
A few questions, answered
How can I check the default inputs by hand?
Semiaxes 5 and 3 place the foci four units from the centre.
Which rule does this calculator apply?
c = √[(a−b)(a+b)], eccentricity = c/a