 # Java Math asin()

The arcsine is the inverse of the sine function.

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

``Math.asin(double num)``

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

## asin() Parameters

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

• num - number whose arc sine is to be returned

Note: The absolute value of num should be always less than 1.

## asin() Return Value

• returns the arcsine of the specified number
• returns 0 if the specified value is zero
• returns `NaN` if the specified number is `NaN` or greater than 1

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

## Example 1: Java Math asin()

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

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

// create variable
double a = 0.99;
double b = 0.71;
double c = 0.0;

// print the arcsine value
System.out.println(Math.asin(a));  // 1.4292568534704693
System.out.println(Math.asin(b));  // 0.7812981174487247
System.out.println(Math.asin(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.asin(a)``

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

## Example 2: Math asin() Returns NaN

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

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

// create variable
double a = 2;

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

// print the arc sine  value
System.out.println(Math.asin(a));  // NaN
System.out.println(Math.asin(b);  // NaN
}
}``````

Here, we have created two variables named a and b.

• Math.asin(a) - returns NaN because value of a is greater than 1
• Math.asin(b) - 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.