Two Triangles Have Six Angles, or Three Pairs
Pencil triangles with a note that two triangles together make six angles
A pencil page with a triangle at the left and, at the right, a rhombus split by its diagonals, with a small triangle sketched below. A short note observes that two triangles together have six angles - that is, three pairs. A separate small construction raises a perpendicular onto a straight segment.
On this page
Counting the angles of two triangles
The note reasons that two triangles have six angles in all, grouped as three binary pairs. The two triangles lettered a - b c and d - e f stand as the illustration of the claim.
Perpendicular raised on a segment
A further small diagram shows a line set at a right angle onto a straight segment, a basic Euclidean construction.