# What is Math acos() function in java?

In java, the arccosine or inverse of cosine can be calculated by using `java.lang.Math.acos()` method. This method from the Math library returns the inverse of cosine between 0 and pi. Furthermore, It takes the angle as an argument and returns arc cos.

## Syntax

``public static double acos(double number)``

## Parameters

`number`: the value whose inverse cosine will be computed.

## Return value

The arc cos of argument value as a number. If the value NaN or infinity is passed in the argument. It’ll return NaN because the absolute value of NaN is greater than 1.

## Explanation

In this example, we’ll be elaborating on `acos()` function which takes a double type value as an argument and returns the inverse of that number.

```class AlgoIdeas {
public static void main( String args[] ) {
// passing positive infinity as an argument
double ans = Math.acos(Double.POSITIVE_INFINITY);
System.out.println("acos(∞) = " + ans);
// passing NaN value as an arguemnt
ans = Math.acos(Double.NaN);
System.out.println("acos(NaN) = " + ans);
// passing +1 as an arguemnt
ans = Math.acos(1);
System.out.println("acos(1) = " + ans);
// passing 0 as an arguemnt
ans = Math.acos(0);
System.out.println("acos(0) = " +  ans);
// passing 3/2 value as an arguemnt
ans = Math.acos(3/2);
System.out.println("acos(3/2) = " + ans);
//passing -1 as an arguemnt
ans = Math.acos(-1);
System.out.println("acos(-1) = " + ans);
// passing NaN value as an arguemnt
ans = Math.acos(0.9);
System.out.println("acos(0.9) = " + ans);
}
}
```

Output

The above program will generate the following output when executed.