# Java Math acos() method with Examples

• Last Updated : 05 Apr, 2018

The java.lang.Math.acos() returns the arc cosine of an angle in between 0.0 and pi. Arc cosine is also called as inverse of a cosine.If the argument is NaN or its absolute value is greater than 1, then the result is NaN.

Syntax :

```public static double acos(double a)
Parameter :
a : the value whose arc cosine is to be returned.
Return :
This method returns the arc cosine of the argument.```

Example :To show working of java.lang.Math.acos() method.

 `// Java program to demonstrate working``// of java.lang.Math.acos() method``import` `java.lang.Math;`` ` `class` `Gfg {`` ` `    ``// driver code``    ``public` `static` `void` `main(String args[])``    ``{``        ``double` `a = Math.PI;`` ` `        ``// Output is NaN, because Math.PI gives 3.141 value``        ``// greater than 1``        ``System.out.println(Math.acos(a));`` ` `        ``// convert Math.PI to radians``        ``double` `b = Math.toRadians(a);`` ` `        ``System.out.println(Math.acos(b));`` ` `        ``double` `c = ``1.0``;``        ``double` `d = ``0.0``;``        ``double` `e = -``1.0``;``        ``double` `f = ``1.5``;`` ` `        ``System.out.println(Math.acos(c));``        ``System.out.println(Math.acos(d));``        ``System.out.println(Math.acos(e));``  ` `       ``// value of f does not lie in between -1 and 1 ``       ``// so output is NaN``        ``System.out.println(Math.acos(f));``    ``}``}`

Output:

```NaN
1.5159376794536454
0.0
1.5707963267948966
3.141592653589793
NaN
```
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