Math.sqrt()

Math.sqrt(input_number)

System.out.println(Math.sqrt(4));    //2.0
System.out.println(Math.sqrt(25));   //5.0
System.out.println(Math.sqrt(-144)); //NaN
System.out.println(Math.sqrt(129));  //11.357816691600547
System.out.println(Math.sqrt(75.65)); //8.697700845625814