Math.Atan() is an inbuilt Math class method which returns the angle whose tangent is given as a double value argument. If the argument is
NaN, then the result will be
NaN.
Syntax:
public static double Atan(double num)
Parameter:
num: It is the number that represents a tangent and type of this parameter is System.Double.
Return Type: Returns an angle Θ, measured in radians and its type is
System.Double. Here the angle is always measured in radians, such that -π/2 ≤ Θ ≤ π/2.
Examples:
Input : Math.Atan(1)
Output : 0.785398163397448
Input : Math.Atan(0.0)
Output : 0
Input : Math.Atan(-0.0)
Output : 0
Input : Math.Atan(Double.PositiveInfinity)
Output : 1.5707963267949
Input : Math.Atan(Double.NegativeInfinity)
Output : -1.5707963267949
Program: To illustrate the Math.Atan() method
Output:
1.26262725567891
0.785398163397448
0
0
1.5707963267949
-1.5707963267949
NaN
Reference: https://learn.microsoft.com/en-us/dotnet/api/system.math.atan?redirectedfrom=MSDN#System_Math_Atan_System_Double_ 
