The signs +, and arithmetic. R., right angle. Def., definition. F.P., fundamental proposition. Ax., axiom. Hyp., hypothesis. Cor., corollary. Ex., exercise. Adj., adjacent. Sup., supplementary. Ext., exterior. Int., interior. Alt., alternate. Pt., point. Pts., points. e.g., for example.. -,×, have the same meaning as in algebra GREEK LETTERS FREQUENTLY USED IN a, pronounced alpha. B, pronounced beta. y, pronounced gamma. NAMING ANGLES 8, pronounced delta. 6, pronounced theta. , pronounced phi. X PLANE GEOMETRY CHAPTER I FUNDAMENTAL NOTIONS AND ELEMENTARY THE STRAIGHT LINE USE OF THE STRAIGHTEDGE 1. If we wish to draw a straight line, we require (1) a plane (flat surface) on which to draw the line, and (2) a straightedge for a guide. The plane may be represented by the surface of a blackboard or by the surface of a sheet of paper lying on a table; and the straightedge by the edge of an ordinary ruler, T-square, or draftsman's triangle (Figs. 1 and 2). 2. Test of a straightedge. Through two convenient points A and B, trace a line on a sheet of paper or other flat surface, using the edge of the ruler, or other instrument to be tested as a guide. Then reverse the ruler end for end (keeping the same side uppermost) and again trace a line through the points A and B. If the two traces are identical whatever be the position of the ruler, provided only the traces pass through the given points, the edge of the ruler is straight. This test depends on the following fundamental properties of a straight line and plane. FIG. 2. FIG. 1. 1 |