Converts x
to a double and returns its arc cosine in radians.
Returns a value in the range 0..PI, or NaN if x
is outside the range -1..1.
external double acos(num x);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-math/acos.html