Euclid's Elements (Jihe Yuanben), Vol 6

Equal Volume 1, 38. Similarly, it is evident that the triangles Ding-Wu-Ji, Ding-Ji-Chou, and Ding-Chou-Yin are also equal. Thus, if the base line Zi-Bing is many times greater than Yi-Bing, then the triangle Jia-Zi-Bing is also that many times greater than Jia-Yi-Bing. Similarly, the multiple of Wu-Yin to Wu-Ji is equal to the multiple of Ding-Wu-Yin to Ding-Wu-Ji because the ratio of the base line segments is equal to the ratio of the figures. Therefore, using the method of three, if the base Zi-Bing is greater than the base Wu-Yin, the triangle Jia-Zi-Bing is also greater than the triangle Ding-Wu-Yin; if they are equal, they are equal; if smaller, they are smaller Volume 1, 38. Thus, the ratio of 1, the base Yi-Bing multiplied to form Zi-Bing, and 3, the triangle Jia-Yi-Bing multiplied to form Jia-Zi-Bing, is equal in size and type to the ratio of 2, the base Wu-Ji multiplied to form Wu-Yin, and 4, the triangle Ding-Wu-Ji multiplied to form Ding-Wu-Yin.