"A diameter of the circle is any straight line drawn through the center and terminated in both directions by the circumference of the circle, and such a straight line also bisects the circle."

"Similar triangles are to one another in the duplicate ratio of their corresponding sides."

"If two triangles have two sides equal to two sides respectively, and have the angles contained by the equal straight lines equal, they will also have the base equal to the base, the triangle will be e…"

"Rectilineal figures are those which are contained by straight lines..."

"Things which are equal to the same thing are also equal to one another."