“ Section 49 The area of a plane is how many square cubits, square handbreadths, or square finger-lengths are contained inside, whether the plane is square, circle, triangle, or any other shape imaginable. ”

“ Section 66 All the angles of a square, summed together, equal 360 degrees. If one draws a line diagonally from one corner of the square to the other corner the square has been divided into a triangle. If so, it is shown to contain 180 degrees twice. A pentagon contains 180 degrees three times, for it can be divided into three triangles. A hexagon contains 180 degrees four times. The general rule is that if one subtracts two sides from the total number of sides of any shape the result is the number of times in contains 180 degrees. ”

“ Section 50 The area of a square is well known, as it is the multiplication of the vertical edge by the horizontal edge.
Section 51 In an ‘even footed’ (isosceles) triangle, the angles opposite the equal edges are themselves equal. For example, in triangle ABC, side AB is equal to AC, and angle ABE is equal to ACE. The proof to this is that if isosceles triangle BCD is constructed on the opposite side of line BC, and line AD is shared as a side of both triangles ABD and ACD, angles BAD and CAD will be equal to each other, as demonstrated in section 23. ”