3BSD was released at the end of 1979 according to wikipedia, and that's just the oldest BSD source I could find, so it may have been in even older versions.
Before ANSI/ISO C I don't think there was really a "math.h" to look for - as it may be different on different systems, but as so many things derive from BSD I wouldn't be surprised if it was "de-facto" standardised to what that supported.
https://web.archive.org/web/20161223125339/http://flash-gord...
...but I wonder when it first hit the scene.