Definition:Pyramid/Apex
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Definition
The vertex of a pyramid which is the common vertex of its triangular faces is called the apex of the pyramid.
In the above diagram, $Q$ is the apex.
Also known as
The apex of a pyramid is seen in some sources as vertex.
Also see
- Definition:Apex of Tetrahedron: all the faces of a tetrahedron are triangular, so this definition cannot apply as it stands.
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, whose plural is vertices.
Hence the colloquial phrase base over apex as the description of a particularly flamboyant physical tumble.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): apex (plural apices)
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): apex (plural apices)