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# Ch. 1: Some History

Ch. 1: Some History. References Modern Geometries: Non-Euclidean, Projective, and Discrete 2 nd ed by Michael Henle Euclidean and Non-Euclidean Geometries: Development and History 4 th ed by Marvin Jay Greenberg A Short History of Geometry , http://geometryalgorithms.com/history.htm.

## Ch. 1: Some History

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1. Ch. 1: Some History References Modern Geometries: Non-Euclidean, Projective, and Discrete2nd ed by Michael Henle Euclidean and Non-Euclidean Geometries: Development and History4th ed by Marvin Jay Greenberg A Short History of Geometry, http://geometryalgorithms.com/history.htm

2. Shocking Possibilities • “The effect of the discovery of hyperbolic geometry on our ideas of truth and reality have been so profound,” wrote the great Canadian geometer H.S.M. Coxeter, “that we can hardly imagine how shocking the possibility of a geometry different from Euclid’s must have seemed in 1820.” (Greenberg, xxv)

3. Ancient Egyptians • “geometry” comes from the Greek geometrein • geo – “earth” • metrein – “to measure” • Herodotus (Greek, 5th cent. B.C.) : Egyptian surveyors originated geometry • Construction of the pyramids • Egyptian geometry: collection of rules for calculation (some correct, some incorrect) without justification

4. Babylonians • More interested in arithmetic (used base 60) • Had calculations for areas and volumes • Pythagorean theorem • Corresponding sides of similar triangles are proportional • 360o in a circle

5. Ancient India • Shapes and sizes of altars and temples • Sulbasutra (2000 B.C.) contains Pythagorean theorem • The number zero!

6. Ancient Chinese • Jiuzhang suanshu (Nine Chapters on the Mathematical Arts) • Surveying, agriculture, engineering, taxation • Pythagorean theorem with a diagram to help explain why it is correct

7. Knowledge of these ancient civilizations • Calculate the area 0f simple rectilinear shapes • The ratio of circumference to diameter in circles is constant & rough approximations of that constant • The area of a circle is half the circumference times half the diameter • Developed to solve practical problems • Evolved out of experiments

8. Ancient Greeks • Thales of Miletus (6th cent. B.C.) • Development of theorems with proofs about abstract entities • Dialectics: the art of arguing well

9. Greek Mathematicians • Pythagoras of Samos (569-475 BC) • Hippocrates of Chios (470-410 BC) • Plato (427-347 BC) • Theaetetus of Athens (417-369 BC) • Eudoxus of Cnidus (408-355 BC) • Euclid of Alexandria (325-265 BC) • Archimedes of Syracuse (287-212 BC) • Hypatia of Alexandria (370-415 AD)

10. Euclid of Alexandria (325-265 BC) • The Elements • I-IV, VI : plane geometry • XI-XIII : solid geometry • V: Eudoxus’ theory of proportions • VII-IX : the theory of whole numbers • X : Theatetus’ classification of certain types of irrationals

11. Euclid’s Postulates (Henle, pp. 7-8) • A straight line may be drawn from a point to any other point. • A finite straight line may be produced to any length. • A circle may be described with any center and any radius. • All right angles are equal. • If a straight line meet two other straight lines so that as to make the interior angles on one side less than two right angles, the other straight lines meet on that side of the first line.

12. Further Developments • Rene Descartes (1596-1650) • Pierre de Fermat (1601-1665) • Girard Desargues (1591-1661) • Blaise Pascal (1623-1662) • Leonhard Euler (1707-1783) • Carl Friedrich Gauss (1777-1855) • Hermann Grassmann (1809-1877) • Arthur Cayley (1821-1895) • Bernhard Riemann (1826-1866) • Felix Klein (1849-1925) • David Hilbert (1862-1943) • Donald Coxeter (1907-2003)

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