Proposition: Prop. 13.01: Area of Square on Greater Segment of Straight Line cut in Extreme and Mean Ratio
(Proposition 1 from Book 13 of Euclid's “Elements”)
If a straight line is cut in extreme and mean ratio then the square on the greater piece, added to half of the whole, is five times the square on the half.
* For let the straight line $AB$ have been cut in extreme and mean ratio at point $C$, and let $AC$ be the greater piece.
* And let the straight line $AD$ have been produced in a straight line with $CA$.
* And let $AD$ be made (equal to) half of $AB$.
* I say that the (square) on $CD$ is five times the (square) on $DA$.
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Modern Formulation
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Table of Contents
Proofs: 1
Mentioned in:
Proofs: 1 2
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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