How can i convert double? to double. Math.Sqrt operations : <p>i would like to ask for some help to this code right below this question... i am encountering some error that says "Argument 1: cannot convert double? to double". How can i fix this what should i add?</p>

<pre><code>private void Calculate(string newOperator = null)
    {
        double? result = null;
        double? first = numbers[0] == null ? null : (double?)double.Parse(numbers[0]);
        double? second = numbers[1] == null ? null : (double?)double.Parse(numbers[1]);

        switch (@operator)
        {
            case "÷":
                result = first / second;
                break;
            case "×":
                result = first * second;
                break;
            case "+":
                result = first + second;
                break;
            case "-":
                result = first - second;
                break;
            case "√":
                result = Math.Sqrt(first);
                break;
            case "SIN":
                result = Math.Sin(first);
                break;
            case "COS":
                result = Math.Cos(first);
                break;
            case "TAN":
                result = Math.Tan(first);
                break;
        }
</code></pre>
