This information is part of the Modelica Standard Library maintained by the Modelica Association.
Trigonometric inverse cosine function
Returns the inverse of cos of u, with -1 ≤ u ≤ +1. Argument u needs to be an Integer or Real expression.
The acos function can also be accessed as Modelica.Math.acos.
acos(0) = 1.5707963267949