Proposition: Prop. 11.39: Prisms of Equal Height with Parallelogram and Triangle as Base
(Proposition 39 from Book 11 of Euclid's “Elements”)
If there are two equal height prisms, and one has a parallelogram, and the other a triangle, (as a) base, and the parallelogram is double the triangle, then the prisms will be equal.
* Let $ABCDEF$ and $GHKLMN$ be two equal height prisms, and let the former have the parallelogram $AF$, and the latter the triangle $GHK$, as a base.
* And let parallelogram $AF$ be twice triangle $GHK$.
* I say that prism $ABCDEF$ is equal to prism $GHKLMN$.
Modern Formulation
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Table of Contents
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References
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"
Adapted from CC BYSA 3.0 Sources:
 Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016