//  benJin:本金    nianLiLV:年利率   month:多少个月
function fangDaiDengErBenXi(benJin, nianLiLv, month) {
    var yueLiLv = nianLiLv / 12
    return benJin * yueLiLv * (Math.pow((1 + yueLiLv), month)) / (Math.pow((1 + yueLiLv), month) - 1)
}