Preface v
PART I EUCLIDEAN GEOMETRY
1 Congruency 3
1.1 Introduction 3
1.2 Congruent Figures 6
1.3 Parallel Lines 12
1.3.1 Angles in a Triangle 13
1.3.2 Thales' Theorem 14
1.3.3 Quadrilaterals 17
1.4 More About Congruency 21
1.5 Perpendiculars and Angle Bisectors 24
1.6 Construction Problems 28
1.6.1 The Method of Loci 31
1.7 Solutions to Selected Exercises 33
1.8 Problems 38
2 Concurrency 41
2.1 Perpendicular Bisectors 41
2.2 Angle Bisectors 43
2.3 Altitudes 46
2.4 Medians 48
2.5 Construction Problems 50
2.6 Solutions to the Exercises 54
2.7 Problems 56
3 Similarity 59
3.1 Similar Triangles 59
3.2 Parallel Lines and Similarity 60
3.3 Other Conditions Implying Similarity 64
3.4 Examples 67
3.5 Construction Problems 75
3.6 The Power of a Point 82
3.7 Solutions to the Exercises 87
3.8 Problems 90
4 Theorems of Ceva and Menelaus 95
4.1 Directed Distances, Directed Ratios 95
4.2 The Theorems 97
4.3 Applications of Ceva's Theorem 99
4.4 Applications of Menelaus' Theorem 103
4.5 Proofs of the Theorems 115
4.6 Extended Versions of the Theorems 125
4.6.1 Ceva's Theorem in the Extended Plane 127
4.6.2 Menelaus' Theorem in the Extended Plane 129
4.7 Problems 131
5 Area 133
5.1 Basic Properties 133
5.1.1 Areas of Polygons 134
5.1.2 Finding the Area of Polygons 138
5.1.3 Areas of Other Shapes 139
5.2 Applications of the Basic Properties 140
5.3 Other Formulae for the Area of a Triangle 147
5.4 Solutions to the Exercises 153
5.5 Problems 153
6 Miscellaneous Topics 159
6.1 The Three Problems of Antiquity 159
6.2 Constructing Segments of Specific Lengths 161
6.3 Construction of Regular Polygons 166
6.3.1 Construction of the Regular Pentagon 168
6.3.2 Construction of Other Regular Polygons 169
6.4 Miquel's Theorem 171
6.5 Morley's Theorem 178
6.6 The Nine-Point Circle 185
6.6.1 Special Cases 188
6.7 The Steiner-Lehmus Theorem 193
6.8 The Circle of Apollonius 197
6.9 Solutions to the Exercises 200
6.10 Problems 201
PART II TRANSFORMATIONAL GEOMETRY
7 The Euclidean Transformations or Isometries 207
7.1 Rotations, Reflections, and Translations 207
7.2 Mappings and Transformations 211
7.2.1 Isometries 213
7.3 Using Rotations, Reflections, and Translations 217
7.4 Problems 227
8 The Algebra of Isometries 231
8.1 Basic Algebraic Properties 231
8.2 Groups of Isometries 236
8.2.1 Direct and Opposite Isometries 237
8.3 The Product of Reflections 241
8.4 Problems 246
9 The Product of Direct Isometries 253
9.1 Angles 253
9.2 Fixed Points 255
9.3 The Product of Two Translations 256
9.4 The Product of a Translation and a Rotation 257
9.5 The Product of Two Rotations 260
9.6 Problems 263
10 Symmetry and Groups 269
10.1 More About Groups 269
10.1.1 Cyclic and Dihedral Groups 273
10.2 Leonardo's Theorem 277
10.3 Problems 281
11 Homotheties 287
11.1 The Pantograph 287
11.2 Some Basic Properties 288
11.2.1 Circles 291
11.3 Construction Problems 293
11.4 Using Homotheties in Proofs 298
11.5 Dilatation 302
11.6 Problems 304
12 Tessellations 311
12.1 Tilings 311
12.2 Monohedral Tilings 312
12.3 Tiling with Regular Polygons 317
12.4 Platonic and Archimedean Tilings 323
12.5 Problems 330
PART III INVERSIVE AND PROJECTIVE GEOMETRIES
13 Introduction to Inversive Geometry 337
13.1 Inversion in the Euclidean Plane 337
13.2 The Effect of Inversion on Euclidean Properties 343
13.3 Orthogonal Circles 351
13.4 Compass-Only Constructions 360
13.5 Problems 369
14 Reciprocation and the Extended Plane 373
14.1 Harmonic Conjugates 373
14.2 The Projective Plane and Reciprocation 383
14.3 Conjugate Points and Lines 393
14.4 Conics 399
14.5 Problems 406
15 Cross Ratios 409
15.1 Cross Ratios 409
15.2 Applications of Cross Ratios 420
15.3 Problems 429
16 Introduction to Projective Geometry 433
16.1 Straightedge Constructions 433
16.2 Perspectivities and Projectivities 443
16.3 Line Perspectivities and Line Projectivities 448
16.4 Projective Geometry and Fixed Points 448
16.5 Projecting a Line to Infinity 451
16.6 The Apollonian Definition of a Conic 455
16.7 Problems 461
Bibliography 464
Index 469
