1. 4 Salmon, G. , A treatise on conic sections (6th edn.), Chelsea (1960). 10.1017/mag.2021.76
2. Lines and Curves
3. 1 Apollonius of Perga, Treatise on Conic Sections, edited by Heath, T. L. , Cambridge University Press (1896), available at https://ia802707.us.archive.org/9/items/treatiseonconics00apolrich/treatiseonconics00apolrich.pdf
4. 3 https://www.cut-the-knot.org/Curriculum/Geometry/ProductInEllipse.shtml#Explanation