# Java - Math acos(double) Method

## Description

The Java Math acos(double a) returns the arc cosine of an angle, in the range of 0.0 through pi.If the argument is NaN or its absolute value is greater than 1, then the result is NaN. A result must be within 1 ulp of the correctly rounded result. Results must be semi-monotonic.

## Declaration

Following is the declaration for java.lang.Math.acos() method

```public static double acos(double a)
```

## Parameters

a − the value whose arc cosine is to be returned.

## Return Value

This method returns the arc cosine of the argument.

NA

## Getting Arc Cosine of an Angle Example

The following example shows the usage of Math acos() method.

```package com.tutorialspoint;

public class MathDemo {

public static void main(String[] args) {

// get a variable x which is equal to PI/2
double x = Math.PI / 2;

// get the arc cosine of x
System.out.println("Math.acos(" + x + ")=" + Math.acos(x));
}
}
```

## Output

Let us compile and run the above program, this will produce the following result −

```Math.acos(0.027415567780803774)=1.5433773235341761
```

## Getting Arc Cosine of a 0° Angle Example

The following example shows the usage of Math acos() method of 0° angle.

```package com.tutorialspoint;

public class MathDemo {

public static void main(String[] args) {

// get a variable x which is equal to zero
double x = 0.0d;

// get the arc cosine of x
System.out.println("Math.acos(" + x + ")=" + Math.acos(x));
}
}
```

## Output

Let us compile and run the above program, this will produce the following result −

```Math.acos(0.0)=1.5707963267948966
```

## Getting Arc Cosine of a 45° Angle Example

The following example shows the usage of Math acos() method of 45° angle.

```package com.tutorialspoint;

public class MathDemo {

public static void main(String[] args) {

// get a variable x which is equal to zero
double x = 45.0d;

// get the arc cosine of x
System.out.println("Math.acos(" + x + ")=" + Math.acos(x));
}
}
```

## Output

Let us compile and run the above program, this will produce the following result −

```Math.acos(0.7853981633974483)=0.6674572160283838
```
java_lang_math.htm