# Definition:Ellipse/Major Axis

< Definition:Ellipse(Redirected from Definition:Major Axis of Ellipse)

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## Definition

Consider an ellipse $K$ whose foci are $F_1$ and $F_2$.

The **major axis** of $K$ is the line segment passing through both $F_1$ and $F_2$ whose endpoints are where it intersects $K$.

In the above diagram, $V_1 V_2$ is the **major axis** of $K$.

### Semi-Major Axis

A **semi-major axis** of $K$ is either half of the major axis of $K$ from its midpoint to its endpoint.

## Also see

## Sources

- 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**major axis**