Euclid's Elements, Book IX, Proposition 19

Proposition 19

[The Greek text of this Proposition is corrupt. However, analogously to Proposition 18 the condition that a fourth proportional to A, B, and C exists is that A measure the product of B and C. ]

Given three numbers, to investigate when it is possible to find a fourth proportional to them.
	Let A, B, and C be the given three numbers. It is required to investigate when it is possible to find a fourth proportional to them.
Q.E.D.

(Forthcoming)

Book IX Introduction - Proposition IX.18 - Proposition IX.20.