 # Java Math atan()

The Java Math atan() method returns the arc tangent of the specified value.

The arc tangent is the inverse of the tangent function.

The syntax of the `atan()` method is:

``Math.atan(double num)``

Here, `atan()` is a static method. Hence, we are accessing the method using the class name, `Math`.

## atan() Parameters

The `atan()` method takes a single parameter.

• num - number whose inverse tangent function is to be returned

## atan() Return Value

• returns the inverse tangent of the specified number
• returns 0 if the specified value is zero
• returns `NaN` if the specified number is `NaN`

Note: The returned value is an angle between -pi/2 to pi/2.

## Example 1: Java Math atan()

``````import java.lang.Math;

class Main {
public static void main(String[] args) {

// create variable
double a = 0.99;
double b = 2.0;
double c = 0.0;

// print the arc tangent value
System.out.println(Math.atan(a));  // 0.7803730800666359
System.out.println(Math.atan(b));  // 1.1071487177940904
System.out.println(Math.atan(c));  // 0.0
}
}``````

In the above example, we have imported the `java.lang.Math` package. This is important if we want to use methods of the `Math` class. Notice the expression,

``Math.atan(a)``

Here, we have directly used the class name to call the method. It is because `atan()` is a static method.

## Example 2: Math atan() Returns NaN

``````import java.lang.Math;

class Main {
public static void main(String[] args) {

// create variable
// square root of negative number
// results in not a number (NaN)
double a = Math.sqrt(-5);

// print the arc tangent  value
System.out.println(Math.atan(a));  // NaN
}
}``````

Here, we have created a variable named a.

• Math.atan(a) - returns NaN because square root of a negative number (-5) is not a number

Note: We have used the Java Math.sqrt() method to compute the square root of a number.