Equal triangles and the squares upon their bases
A Pythagorean-style proof, following the close of the 'multiple' definition
The page first finishes the definition of the 'multiple', which is said relatively to the whole, the whole relation lying between the two extremes. It then gives a geometric proof: the triangles i c b and c a d are equal because their bases and sides are sides of the squares c a h i and d c b e. Leonardo concludes that the squares a c h i and c d K L, being double those triangles on the same bases and between the same parallels, are themselves equal.
On this page
Close of the definition of the multiple
The multiple is said relatively to the whole, and in the two extremes lies their entire relation. This completes the definition begun on the preceding page.
Triangles i c b and c a d proved equal
The triangles i c b and c a d are shown equal because base i c equals base c a (they are sides of the square c a h i) and side c b equals side c d (they are sides of the square d c b e).
Squares a c h i and c d K L are equal
Since the two triangles are equal, the squares a c h i and c d K L are equal as well, for each is double its triangle, standing on the same bases i c and c a and between the parallels i c h b and c d a L.