atan
Computes the arc tangent of the value x;
the returned value is an angle in the range from -PI/2 to PI/2 radians.
Special cases:
atan(NaN)isNaN
Computes the arc tangent of the value x;
the returned value is an angle in the range from -PI/2 to PI/2 radians.
Special cases:
atan(NaN) is NaN