ACOS
SQL> select ACOS(1) from dual;
ACOS(1)
----------
0
SQL> select ACOS(-1) from dual;
ACOS(-1)
----------
3.14159265
SQL>
SQL> select ACOS(1) from dual;
ACOS(1)
----------
0
SQL> select ACOS(-1) from dual;
ACOS(-1)
----------
3.14159265
SQL>