quod erat demonstrandum

American  

[kwawd e-raht dey-mawn-strahn-doom, kwod er-uht dem-uhn-stran-duhm] / kwɔd ˈɛ rɑt ˌdeɪ mɔnˈstrɑn dʊm, kwɒd ˈɛr ət ˌdɛm ənˈstræn dəm /

Latin.

1. which was to be shown or demonstrated.

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quod erat demonstrandum British  

/ ˈkwɒd ˈɛræt ˌdɛmənˈstrændʊm /

1.  QED.  (at the conclusion of a proof, esp of a theorem in Euclidean geometry) which was to be proved

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quod erat demonstrandum Cultural  

1. A phrase used to signal that a proof has just been completed. From Latin, meaning “that which was to be demonstrated.”

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Example Sentences

He might usefully have concluded his column with the letters we had to put next to solved mathematical equations: QED — quod erat demonstrandum — just to prove his point.

From Washington Post

QED: quod erat demonstrandum, Latin for “which was to be demonstrated or proved.”

From Literature

“Burning Bush” joins the ranks of other recent films from the former Eastern Bloc — like “Ida” from Poland, “Quod Erat Demonstrandum” from Romania, “Barbara” from Germany — that try to grasp, with the benefit of hindsight but without too much ex post facto gloating, the logic of Communist dictatorship.

From New York Times

Queen's Counsel; Queen's College. q.d., quasi dicat=As if he should say. q.e., quod est=Which is. q.e.d., quod erat demonstrandum=Which was to be demonstrated. q.e.f., quod erat faciendum=Which was to be done. q.e.i, quod erat inveniendum=Which was to be found out. q.l., quantum libet=As much as you please.

From Project Gutenberg

Each marked a step in ratiocination or a rise in interest in the matter that engaged his mind until the climax of proof or animation was reached, when he would begin to untie them, one after the other, timing the process so judiciously that "Amen!" or "Quod erat demonstrandum!" passed his lips as the released cambric swept through his hand in a flourish prior to its restoration to his pocket.

From Project Gutenberg