addJavascript = function(fileName) {
	var th = document.getElementsByTagName('head')[0];
	var s = document.createElement('script');
	s.setAttribute('type','text/javascript');
	s.setAttribute('src',fileName);
	th.appendChild(s);
}
addStylesheet = function(fileName) {
	var th = document.getElementsByTagName('head')[0];
	var s = document.createElement('link');
	s.setAttribute('type','text/css');
	s.setAttribute('rel','stylesheet');
	s.setAttribute('href',fileName);
	th.appendChild(s);
}
car_calculate = function()
{
	var price = document.getElementById("car_purchaseprice").value;
	if ( price.length == 0 )
	{
		alert("Please enter the purchase price");
		return;
	}
	price = fixNumber(price);
	price = parseFloat(price);
	if ( isNaN(price) )
	{
		alert("Please enter the  purchase price as a number");
		return;
	}
	if ( price < 0 )
	{
		alert("Please enter a purchase price >= 0");
		return;
	}
	
	var rate = document.getElementById("car_rate").value;
	if ( rate.length == 0 )
	{
		alert("Please enter an interest rate");
		return;
	}
	rate = fixNumber(rate);
	rate = parseFloat(rate);
	if ( isNaN(rate) )
	{
		alert("Please enter the interest rate as a number");
		return;
	}
	if ( rate < 0 || rate >= 35 )
	{
		alert("Please enter a interest rate >= 0 and less than 35");
		return;
	}

	var months = document.getElementById("car_duration").value;
	if ( months.length == 0 )
	{
		alert("Please enter the # of months you loan will last");
		return;
	}
	months = fixNumber(months);
	months = parseFloat(months);
	if ( isNaN(months) )
	{
		alert("Please enter the # of months as a number");
		return;
	}
	if ( months <= 0 || months > 120 )
	{
		alert("Please enter a # of months between 1 and 120");
		return;
	}

	var downpayment = document.getElementById("car_down").value;
	if ( downpayment.length == 0 )
	{
		alert("Please enter a down payment");
		return;
	}
	downpayment = fixNumber(downpayment);
	downpayment = parseFloat(downpayment);
	if ( isNaN(downpayment) )
	{
		alert("Please enter the down payment as a number");
		return;
	}
	if ( downpayment < 0 )
	{
		alert("Please enter a down payment >= 0");
		return;
	}
	if ( downpayment >= price )
	{
		alert("Your down payment exceeds the car price, so you won't need a loan.");
		return;
	}
	
	var mrate = rate / 1200;

	var loanamount = price - downpayment;
	var payment;

	if ( rate == 0 )
	{
		payment = loanamount / months;
	}
	else
	{
		var factor = Math.pow(1 + mrate, months );
		payment = loanamount * ( mrate / (1 - 1/factor) );
	}
	
	var x = document.getElementById("car_dt_results");

	var results = "<p>The amount of your loan will be <b>" + formatDollars(loanamount) + "</b>.";

	results += "<p>Your monthly payment will be <b>" + formatDollars(payment) + "</b>.";
	
	results += "<p>You will pay a total of <b>" + formatDollars(((payment * months) + downpayment) - price) + "</b> in interest.";
	
	x.innerHTML = results;
	x.style.display = "block";
}