Euclid's Elements (Jihe Yuanben), Vol 6

Geng-Jia original derivation is, according to this, the same as the ratio of Jia-Yi to Yi-Bing and also as Jia-Geng to Geng-Wu.
Flattening this, it is as Yi-Ji to Yi-Bing and as Ding-Geng to Geng-Wu Book 5, Proposition 22.

Proposition 5

If the ratios of the two sides of two triangles are equal, then the two figures are equiangular, and the angles opposite the respective similar sides are equal.

Explanation: Let there be two triangles, Jia-Yi-Bing and Ding-Wu-Ji. If the ratios of their sides are equal—that is, if Jia-Yi to Yi-Bing is as Ding-Wu to Wu-Ji, and Yi-Bing to Jia-Bing is as Wu-Ji to Ding-Ji, and Jia-Bing to Jia-Yi is as Ding-Ji to Ding-Wu—it is stated that these two figures are equiangular and...