# 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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