The guy's describing and drawing his solution to a flat trapezoid. Two triangles.
So we have two documents, Rhind and Moscow.
One's talking about triangles and cylinders the other about flat trapezoids, (two triangles).
To be frank he's making quite a good job of figuring them out without the benefit classical trigonometry.
Reminds me of me in a math exam when I haven't revised.
They're geometry textbooks.
No more, no less.
Possible uses.. Land surveying.. Stone cutting.. General Construction.. Or just ancient geekery..??