Euler Formula -- from Wolfram MathWorld
https://mathworld.wolfram.com/EulerFormula.html17.12.2021 · The Euler formula, sometimes also called the Euler identity (e.g., Trott 2004, p. 174), states e^(ix)=cosx+isinx, (1) where i is the imaginary unit. Note that Euler's polyhedral formula is sometimes also called the Euler formula, as is the Euler curvature formula. The equivalent expression ix=ln(cosx+isinx) (2) had previously been published by Cotes (1714).