Comparing the Angles of Similar Right Triangles
If angle a exceeds angle d, the base cd exceeds fe, worked through many triangles
The folio compares triangles, positing "that angle a is larger than d" and concluding that "base cd is larger than fe." Two similar right triangles, lettered a b c and d e f, head the argument, followed by a right triangle d e f cut by a line from vertex d and a pair of adjacent triangles f, g, k. Around these, seven further attempts at combining triangles are sketched, and pen-strokes link the figures to triangles continued on the facing folio. A short marginal note reads "it is helped and defines."
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If angle a > d then base cd > fe
Two similar right triangles lettered a b c and d e f are set up with similarity marks on two sides. The claim posits "that angle a is larger than d" and concludes "base cd is larger than fe."
Right triangle d e f cut from a vertex
A further right triangle lettered d, e, f has a line drawn from vertex d producing a second angle, continuing the comparison of angles and bases.
Adjacent triangles f, g, k and further attempts
A pair of adjacent triangles is lettered f, g, k, with two sides marked as equal by pen-strokes. Seven more attempts at triangle combinations are arranged around the figure and tied by strokes to the facing folio.