-399 pythagorean's discover irrational numbers -240 Eratosthenes determines circumference of earth -230 Archimedes determines fromulas for the area of a section of a parabola formulas forthe area of a section of a parabola -200 Apollonius studies conic sections -200 Euclid writes Elements -100 Hipparchus develops the trig tables 825 Al-Khwarizmi uses Zero 1525 Rudolf f introduces the radical sign 1535 Tartaglia solves cubic equations 1545 Square roots of negative numbers 1557 Record introduces the equals sign 1565 Goldbach states famous conjecture 1614 Napier invents logarithms 1614 Briggs uses base 10 logarithms 1621 Harriet introduces the inequality signs 1630 Ought red invents the slide rule 1637 Descartes creates analytic geometry 1641 Descartes' Geometric was published 1654 Pascal and Fermat discuss theory of probability in their correspondence 1655 Wallis introduces the symbol for infinity 1660 Fermat leaves last theorem 1665 Newton invents calculus 1669 Barrow discovered the general solution for the tangent line to a curve 1675 Leibniz invents calculus 1696 L'Hopital wrote the first text on differential calculus 1715 Brook Taylor's published account of polynomial approximations of trans cental functions 1742 Goldbach states famous conjecture 1748 Agnes i writes Foundations of Analysis 1755 Euler shows that ePi i + 1 = 0 that epi i +1 = 0 1770 Lambert proves pi is irrational 1773 Sac cheri writes Euclid Freed of Every Flaw 1797 Lagrange proved the Mean Value Theorem 1814 Arg and graphs imaginary numbers 1828 Gauss determines the convergence of infinite series 1830 Galois writes about group theory 1842 Lovelace describes how to program Babbage's "Analytical Engine" 1854 Riemann creates elliptic geometry 1854 Cayley uses matrices in solving equations 1858 Mobius strip is discovered 1888 Kovalevsky is the first woman to earn a doctorate in mathematics 1895 Cantor creates transfinite numbers 1905 Einstein publicly formulated his theory on relativity 1910 Whitehead and Russell write Principia Mathematica 1919 Alice Hamilton is Harvard's first female professor 1931 Godel publishes "incompleteness" theorems 1942 EN IAC, the first electronic computer is invented 1974 Mrs. Greminger became a mathematics instructor at Valle High School 1975 Bill Gates started his computer company Microsoft 1976 Four color map problem is solved 1998 Mrs. Moll became a mathematics instructor at Valle High School.