Two pentagons and three measured triangles
Each pentagon split into three triangles; sides 3-4-5, 6-8-10, 12-16-20
In faint pencil the sheet shows two pentagons at the top, each divided from a single vertex into three triangles. Below stand three triangles annotated with the lengths of their sides, the sets 3, 4, 5; 6, 8, 10; and 12, 16, 20, a study of similar right triangles whose sides double in scale. A pencil page-number (181) sits in the upper corner.
On this page
Two pentagons each divided into three triangles
Two pentagons are drawn side by side, each split from one vertex into three triangles. The construction breaks the five-sided figure into a fan of triangular parts.
Three triangles with proportional side-measures
The three lower triangles carry the side-lengths 3, 4, 5; 6, 8, 10; and 12, 16, 20. Each set doubles the one before it, giving similar triangles in continued proportion.