8. Ren´e Descartes (1596-1650) was a philosopher whose work, La G´eom´etrie, includes his application of algebra to geometry from which we now have Cartesian geometry. Descartes was pressed by his friends to publish his ideas, and he wrote a treatise on science under the title “Discours de la m´ethod pour bien conduire sa raison et chercher la v´erit´e dans les sciences”. Three appendices to this work were La Dioptrique, Les M´et´eores, and La G´eom´etrie. The treatise was published at Leiden in 1637. Descartes associated imaginary numbers with geometric impossibility. This can be seen from the geometric construction he used to solve the equation z2 = az −b2, with a and b2 both positive. According to [1],Descartes coined the term imaginary:
“For any equation one can imagine as many roots [as its degree would suggest], but in many cases no quantity exists which corresponds to what one imagines.”