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major axis

The longer axis of an ellipse, running through both foci; length 2a.

The major axis of an ellipse is the longer of its two axes of symmetry, running through the center and both foci, with endpoints at the vertices (\pm a,0) (or the corresponding vertical pair) and total length 2a. The foci always sit on the major axis, never the minor axis.

See also

minor axis focus (of a conic)
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