In the 18th century, Leonhard Euler's "Introductio in analysin infinitorum" (1748) was mostly responsible for establishing the analytic treatment of trigonometric functions in Europe, deriving their infinite series and presenting "Euler's formula" "e""ix" = cos "x" + "i" sin "x".
L'"Introductio in analysin infinitorum" (1748) di Leonardo Eulero ebbe il merito di stabilire la moderna trattazione analitica delle funzioni trigonometriche in Europa, definendole tramite serie infinite e presentando la formula di Eulero "e""ix" = cos("x") + "i" sin("x").