Alarcón Vasco, Sergio; Suescún, Carlos Mario Descartes’ method for determinig the tangent to a curve. (El método de Descartes para determinar la tangente a una curva.) (Spanish. English summary) Zbl 1329.01019 Mat., Enseñ. Univ. (N.S.) 19, No. 1, 103-114 (2011). The paper transcribes the construction of the normal line to a circle, to an ellipse and to a parabola at a given point, found in Descartes’ La géometrie. In the last part, the authors apply Descartes’ method with contemporary notation for the construction of the normal line to a cubic function, although they state that its application can be performed for a general algebraic function. Reviewer: Maria Rosa Massa Esteve (Barcelona) MSC: 01A45 History of mathematics in the 17th century 00A35 Methodology of mathematics 97D99 Education and instruction in mathematics Keywords:normal line to a curve; circle method PDFBibTeX XMLCite \textit{S. Alarcón Vasco} and \textit{C. M. Suescún}, Mat., Enseñ. Univ. (N.S.) 19, No. 1, 103--114 (2011; Zbl 1329.01019)