To return the arctangent of x, when x is expressed in radians.
The result is within the range of -π/2 to π/2.
The expression x may be any numeric type. The evaluation of ATN is performed in single precision unless the /d switch is used when GW-BASIC is executed.
To convert from degrees to radians, multiply by π/180.
10 INPUT X 20 PRINT ATN(X) RUN ? 3 1.249046
Prints the arctangent of 3 radians (1.249046).