\begin{definition}[Definition:Ellipse/Major Axis]
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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 $K$.
\end{definition}