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 http://aleph0.clarku.edu/~djoyce/java/elements/bookI/propI1.html - Doctor Rick, The Math Forum http://mathforum.org/dr.math/
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