Associated Topics || Dr. Math Home || Search Dr. Math

When is the expression Q.E.D. used?

```
Date: 02/15/99 at 22:51:36
From: Andrea
Subject: When is the expression QED used?

I need to know when and why QED is used in a proof.

```

```
Date: 02/16/99 at 08:27:06
From: Doctor Rick
Subject: Re: When is the expression QED used?

Q.E.D. stands for the Latin "quod erat demonstrandum", which means
"which was to be demonstrated (or proved)". It appears after the final
step of the proof, which will be the statement that you originally set
out to prove.

You will also find Q.E.F. at the end of a construction. This stands
for "quod erat faciendum", "which was to be done (or made)".

For examples, see Euclid's Elements. His first proposition is a
construction, and ends in Q.E.F.; in this online edition, notes after
the proposition explain the use of Q.E.D. and Q.E.F.

Euclid's Elements, Book I, Proposition 1 - David Joyce
http://aleph0.clarku.edu/~djoyce/java/elements/bookI/propI1.html

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Definitions
High School Euclidean/Plane Geometry
High School Geometry
Middle School Definitions
Middle School Geometry
Middle School Two-Dimensional Geometry

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search