費馬的方法不叫微分法，叫adequality，中文的水平太低犯錯誤，adequality沒有中文翻譯詞

Fermat's method

Fermat used adequality first to find maxima of functions, and then adapted it to find tangent lines to curves.

To find the maximum of a term ${\displaystyle px}$, Fermat equated (or more precisely adequated) ${\displaystyle px}$ and ${\displaystyle pxe}$ and after doing algebra he could cancel out a factor of ${\displaystyle e}$and then discard any remaining terms involving ${\displaystyle e}$ ${\displaystyle {\mathrm{}}^{}}$
${\displaystyle {\mathrm{}}^{}}$

https://en.wikipedia.org/wiki/Adequality