Commentary on Proposition VII.13

Back to Proposition VII.13.

[Folio 0319 | p. 313]

$$ \begin{aligned} \text{If} \quad & a : b = c : d, \\ \text{then, alternately,} \quad & a : c = b : d. \end{aligned} $$

The proposition corresponds to V. 16 for magnitudes, and the proof consists in connecting VII. Def. 20 with the result of VII. 10.