# Java Math acos() method with Examples

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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