Descartes, Rene (1596-1650)
Descartes was one of the greatest philosophers in the 6th century. He was French, born in Touraine in north-west France and was educated at a Jesuit college. When he was 25, he decided to devote his life to the study of scientific and philosophic subjects. He traveled to Holland and Sweden. He never married and died at Stockholm of inflammation of the lungs.
Descartes believed in the existence of the things. He realized the necessity of depending on the experience instead of human senses.
Beside his contributions in the field of philosophy, Descartes produced great contributions in the field of Calculus. He and a French lawyer, Pierre Fermat (1601-1665)are considered the inventors of analytic geometry. It was Descartes and Fermat who introduced the point of view that is characteristic of analytic geometry. They considered curves defined by equations as well as by geometric properties. In addition, they made extensive use of the close association between algebra of equations and the geometry of the curves.
Descartes and Fermat used only what corresponds to the positive half of the modern horizontal coordinate axis and did not use an explicit vertical axis. To plot a point corresponding to positive solutions of an equation in two unknowns A and E Fermat measured the distance A along a horizontal line from a fixed point. The fixed point corresponded to the origin in a modern coordinate plane. He then measured the distance E along a line at a fixed angle, but not necessarily a right angle, to the horizontal line.
Descartes' procedure for associating solutions of equations in two unknowns to points in a plane was similar to Fermat's. He also used occasionally what would correspond to the fourth quadrant of a modern coordinate plane, in that he allowed negative values of the second unknown.
In the 1630ís, Descartes devised a method for finding normal lines to certain curves by studing the solutions of polynomial equations.