The 9 below all use Euclid's fifth axiom in their proof. The form of Euclid's fifth postulate given below is not actually the way that Euclid phrased it, which was rather cumbersome. It is possible to draw one and only one straight line from any point to any point. From each end of a finite straight line it is possible to produce it continuously in a straight line by an amount greater than any assigned length. It is possible to describe one and only one circle with any centre and radius.
All right angles are equal to one another.
Through a given point not on a given straight line, and not on that straight line produced, no more than one parallel straight line can be drawn. A straight line falling on parallel straight lines makes the alternate angles equal to one another, the exterior angle equal to the interior and opposite angle, and the interior angles on the same side equal to two right angles. Straight lines parallel to the same straight line are also parallel to one another. In any triangle, if one of the sides be produced. The exterior angle is equal to the two interior and opposite angles, and the three interior angles of the triangle are equal to two right angles.