Determining whether a number is a Fibonacci number

Question

I need to to write a Java code that checks whether the user inputed number is in the Fibonacci sequence.

I have no issue writing the Fibonacci sequence to output, b

Answer 1

Finding out whether a number is Fibonacci based on formula:

public static boolean isNumberFromFibonacciSequence(int num){

    if (num == 0 || num == 1){
        return true;
    }

    else {
        //5n^2 - 4 OR 5n^2 + 4 should be perfect squares
        return isPerfectSquare( 5*num*num - 4) || isPerfectSquare(5*num*num - 4);
    }
}

private static boolean isPerfectSquare(int num){
        double sqrt = Math.sqrt(num);
        return sqrt * sqrt == num;
}