And
10 A parallelogramme is equall both in his opposite sides, and angles, and segments cut by the diameter.
Or thus: The opposite, both sides, and angles, and segments cut by the diameter are equall. Three things are here concluded: The first is, that the opposite sides are equall: This manifest by the [26 e v]. Because two right lines doe jointly bound equall parallells.
The second, that the opposite angles are equall, the Diagonall ai, doth shew. For it maketh the triangles aei, and ioa, equilaters: And therefore also equiangles: And seeing that the particular angles at a, and i, are equall, the whole is equall to the whole. This part is the 34. p j;
The third: The segments cut by the diameter are alwayes equall, whether they be triangles, or any manner of quadrangles, as in the figures. For the Diameter doth cut into two equall parts, the parallelogramme by the Angles, or by the opposite sides, or by the alternall equall segments of the sides.
And
11. The Diameter of a parallelogramme is cut into two by equall raies.