In a 1727 mathematical compendium, Pierre Varignon (1654-1722) published his solution to the problem of finding the surface area of a scalene (oblique) cone, one whose base is circular but whose vertex is off-center. The article after Varignon's in that publication was by Gottfried Leibniz (1646-1716), who proposed improvements and even extended the solution to a base with any curve. When Leonhard Euler (1707-1783) published on the subject [E133] in 1750, he gently pointed out an error in Leibniz's solution, which he corrected, after extending Varignon's solution in the case of circular base. Euler then used Leibniz's approach to solve the general problem. This paper examines all three articles, including English translations.
Curtin, Daniel J.
"The Surface Area of a Scalene Cone as Solved by Varignon, Leibniz, and Euler,"
Euleriana: 1(1), pp.10-41.
Available at: https://scholarlycommons.pacific.edu/euleriana/vol1/iss1/3