Description

   The acos functions compute the principal value of the arc cosine
   of x in the range [0,pi] radians for x in the domain [-1,1].

   The acosd functions compute the principal value of the arc cosine
   of x in the range [0,180] degrees for x in the domain [-1,1].

   For abs(x) > 1, the value of acos(x) is 0, and errno is set to
   EDOM.