C# | Math.Acos() Method

Math.Acos() is an inbuilt Math class method which returns the angle whose cosine is given as a double value argument. If the argument is NaN, then the result will be NaN.

Syntax:

public static double Acos(double num)

Parameter:

num: It is the number that represents cosine and type of this parameter is System.Double. It must be greater than or equal to -1, but less than or equal to 1.

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 0 ≤ Θ ≤ π.

Note: If the value of the num is greater than 1 or less than -1 or equals to NaN, then this method always returns NaN as result. To convert the radians(return value) to degrees multiply it by 180 / Math.PI.

Examples:

Input  : Math.Acos(2)
Output : NaN

Input  : Math.Acos(0.3584)
Output : 1.20424285296577
     
Input  : Math.Acos(0.0)
Output : 1.5707963267949

Input  : Math.Acos(-0.0)
Output : 1.5707963267949

Input  : Math.Acos(Double.PositiveInfinity)
Output : NaN

Input  : Math.Acos(Double.NegativeInfinity)
Output : NaN

Program: To illustrate the Math.Acos() method

// C# program to demonstrate working
// of Math.Acos() method
using System;

class Geeks {

    // Main Method
    public static void Main(String[] args)
    {
        double a = Math.PI;

        // using Math.Acos() method
        Console.WriteLine(Math.Acos(a));

        // argument is greater than 1
        Console.WriteLine(Math.Acos(2));

        Console.WriteLine(Math.Acos(0.3584));

        double d = 0.0;
        double e = -0.0;
        double posi = Double.PositiveInfinity;
        double nega = Double.NegativeInfinity;
        double nan = Double.NaN;

        // Input positive zero
        // Output 1.5707963267949
        double res = Math.Acos(d);

        // converting to degree
        // i.e output will be 90 degree
        double rest = res * (180 / Math.PI);
        Console.WriteLine(rest);

        // Input negative zero
        // Output 1.5707963267949
        Console.WriteLine(Math.Acos(e));

        // input PositiveInfinity
        // Output NaN
        Console.WriteLine(Math.Acos(posi));

        // input NegativeInfinity
        // Output NaN
        Console.WriteLine(Math.Acos(nega));

        // input NaN
        // Output NaN
        Console.WriteLine(Math.Acos(nan));
    }
}

Output:

NaN
NaN
1.20424285296577
90
1.5707963267949
NaN
NaN
NaN

Reference: https://msdn.microsoft.com/en-us/library/system.math.Acos