But before Descartes is generally viewed. that geometry was euclidean geometry. and that's essentially the geometry that you studied in geometry class in 8th or 9th or 10th grade. in a traditional high school curriculum. and that's the geometry of studying the relationships between triangles, and their angles. and the relationships between circles. and you have radii and then you have triangles inscribed in circles and all the rest and we'll go into some depth in that in the geometry playlist.