as3/javascript贷款公式，用于根据周利率计算原则

我有一个AS3函数来计算每周还款值，只要我有贷款金额、利率和期限的年值

private function calculateRepayment(_loanAmount, _years, _interest):Number
{
    var nWeek = _years * 52;
    var nInterest = _interest/(52*100);
    var nRepayment = ( _loanAmount * nInterest *Math.pow((1+nInterest),nWeek) ) / ( Math.pow((1+nInterest),nWeek)-1 );
    return Number(nRepayment);
}

现在我需要编写一个函数，根据每周还款、利率和年期的值计算贷款金额

private function calculateRepayment(_loanAmount, _years, _interest):Number
{
    var nWeek = _years * 52;
    var nInterest = _interest/(52*100);
    var nRepayment = ( _loanAmount * nInterest *Math.pow((1+nInterest),nWeek) ) / ( Math.pow((1+nInterest),nWeek)-1 );
    return Number(nRepayment);
}

关于转换为AS3或javascript的公式的任何帮助都将非常感谢，我认为理论上这是loanAmount=利率/利率时间

例如：

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好的，我算出了，下面是函数：

private function calculateLoanAmount(_repayment, _years, _interest):Number
{
    var p:Number = _repayment; // weekly payment
    var i:Number = (_interest / 52) * 0.01; // weekly interest factor
    var n:Number = _years * 52; // number of weekly payments - (5 years) 5*52 = 260
    var principal:Number = (p * (1 - 1 / (Math.pow(1 + i, n)))) / i;
    principal = Math.round(roundDec(principal, 0)); // prepare for output
    return Number(principal);
}

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这是我为一个朋友开发的一个flash贷款计算器。它应该是：var nRepayment=\u loanAmount*Math.pow1+nInterest，nWeek/nWeek；也就是说，我不确定这个贷款是如何运作的，在做作业时使用这个链接没有不正确的伪灰尘它应该是var nRepayment:Number=\u loanAmount*nInterest/1-Math.pow1/1+nInterest，nTerm；