## C# Math.Acos() – Examples

In this tutorial, we will learn about the C# Math.Acos() method, and learn how to use this method to find the arc cosine of given double value, with the help of examples.

## Acos(Double)

Math.Acos(d) returns the angle whose cosine is the specified number `d`. The angle returned shall be in radians.

If a value greater than 1 or less than -1 is given as argument, Acos() returns `Double.NaN`.

### Syntax

The syntax of Acos(d) method is

`Math.Acos(Double d)`

where

Return Value

The method returns value of type double.

### Example 1 – Math.Acos(0.5)

In this example, we will find the angle for which cosine value is 0.5. We shall print the result both in radians and in degrees.

We know that cos(60 degrees) = 0.5.

C# Program

```using System;

class Example {
static void Main(string[] args) {
Double d = 0.5;

Double angle = Math.Acos(d);
Console.WriteLine(\$"Angle in degrees : {(180 / Math.PI) * angle}");
}
}```

Output

```Angle in radians : 1.0471975511966
Angle in degrees : 60```

### Example 2 – Math.Acos(1.0)

In this example, we will find the angle for which cosine value is 1.0. We know that cos(0 degrees) = 1.0.

C# Program

```using System;

class Example {
static void Main(string[] args) {
Double d = 1.0;

Double angle = Math.Acos(d);
Console.WriteLine(\$"Angle in degrees : {(180 / Math.PI) * angle}");
}
}```

Output

```Angle in radians : 0
Angle in degrees : 0```

### Example 3 – Acos(0)

In this example, we will find the angle for which cosine value is 0. We know that cos(90 degrees) = 0.

C# Program

```using System;

class Example {
static void Main(string[] args) {
Double d = 0;

Double angle = Math.Acos(d);
Console.WriteLine(\$"Angle in degrees : {(180 / Math.PI) * angle}");
}
}```

Output

```Angle in radians : 1.5707963267949
Angle in degrees : 90```

### Example 4 – Acos(5) – Invalid Argument

In this example, we will find the angle for which cosine value is 5. We know that the range of cos(angle) is [-1.0, 1.0], and since the given argument is out of range, Acos() returns Double.NaN.

C# Program

```using System;

class Example {
static void Main(string[] args) {
Double d = 5;

Double angle = Math.Acos(d);
```Angle in radians : NaN