The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
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.  

Thanks for your help.

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   

- Doctor Rick, The Math Forum   
Associated Topics:
High School About Math
High School Definitions
High School Euclidean/Plane Geometry
High School Geometry
Middle School About Math
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

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.