Definition:Cone/Apex

Definition

Consider a cone consisting of the set of all straight lines joining the boundary of a plane figure $PQR$ to a point $A$ not in the same plane of $PQR$:

In the above diagram, the point $A$ is known as the apex of the cone.

Also known as

The apex of a cone is also known as its vertex.

Also see

• Definition:Base of Cone

Linguistic Note

The plural of apex is apices, which is pronounced ay-pi-seez.

The form apexes can often be seen, but this is technically incorrect.

Compare vertex.

Hence the colloquial phrase base over apex as the description of a particularly flamboyant physical tumble.

Sources

• 1933: D.M.Y. Sommerville: Analytical Conics (3rd ed.) ... (previous) ... (next): Chapter $\text {IV}$. The Ellipse: $1$.
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): Entry: vertex