...describe familiar figures in more or less familiar ways. For example: « When a straight line crossing a straight line makes the adjacent angles equal to one another, each of the equal angles is called a right angle, and the straight line crossing the other is called a perpendicular...

...straight liue, B, makes the adjacent angles equal to one another, each of B Fig. 1. Fig. 2. the angles Ls called a right angle, and the straight line which...stands on the other is called a perpendicular to it (Fig. 2). 8. An obtuse angle is that which is greater than a right angle (Fig. 3). 9- An acute angle...

...containing the angle are straight, the angle is caller rectilinear. 9. When a straight line set up on a straight line makes the adjacent angles equal to one another, each of the angles is right, and the straight line standing on the other is called the perpendicular to the one on which...

...BA is perpendicular to AT and Definition I.10, which states that “When a straight line set up on a straight line makes the adjacent angles equal to one another, each of the right angles is right, and the straight line standing on the other is called a perpendicular to that...

...classes of (rectilinear) angles (trans. Heath 1926, I, 181): 1 0. When a straight line set up on a straight line makes the adjacent angles equal to one another, each of the equal angles is right [...]. 1 1 . An obtuse angle is an angle greater than a right angle. 12. An acute...