When configuring a trigger expression, one of the functions available is atan2(), which has the following, slightly incorrect, description:

The arctangent of the ordinate (exprue) and abscissa coordinates specified as an angle, expressed in radians.

"(exprue)" should be "(value)".

For reference, see: https://www.zabbix.com/documentation/6.0/en/manual/appendix/functions/math