## "cogito ergo sum"## "Je pense, donc je suis"## "I think, therefore I am"René Descartes (1596-1650). René Descartes, a summary |

"The three axes of three-dimensional Cartesian coordinates, conventionally denoted the x-, y-, and z-axes (a notation due to Descartes ) are chosen to be linear and mutually perpendicular .

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In René Descartes' original treatise (1637), which introduced the use of coordinates for describing plane curves, the axes were omitted, and only positive values of the x- and the y-coordinates were considered, since they were defined as distances between points. For an ellipse this meant that, instead of the full picture which we would plot nowadays (left figure), Descartes drew only the upper half (right figure). "