ACOS

Return the inverse cosine value of an input radian value.

ACOS(number)

The return type is a DOUBLE PRECISION number.

For example:
premdb=# select acos(0.10) from sys.const;
       acos       
------------------
 1.47062890563334
(1 row)
premdb=# select acos(avg_att/100) from team order by teamid limit 2;
       acos        
-------------------
 0.927995034405117
  1.22717385372596
(2 rows)