DOUBLE acos(DOUBLE x) Returns the arc cosine of x, or nan if NULL is not in the range -1 to 1.
mysql> select acos(1); +-----------+ | acos(1.0) | +-----------+ | 0 | +-----------+ mysql> select acos(0); +--------------------+ | acos(0.0) | +--------------------+ | 1.5707963267948966 | +--------------------+ mysql> select acos(-2); +------------+ | acos(-2.0) | +------------+ | nan | +------------+
ACOS