Euclid's Elements - Book 8, Proposition 12

Proposition: If A = C^3 and B = D^3, then there exists two numbers H and K such that A:H = H:K =K:B, and A:B is the triplicate ratio of C:D PDFs: https://github.com/sandy-bultena/Euclid/tree/master/Propositions/PDFs