function annuity( rate, nper, pv )
{    
    return ( ( pv * rate ) / ( 1 - Math.pow( (1/(1+rate)), nper) ) );
}

function restLoan( start_loan, interest, payment_number, number_of_payments )
{
    return start_loan* ( ( Math.pow(1+interest,number_of_payments)-Math.pow(1+interest,payment_number) ) / ( Math.pow(1+interest,number_of_payments) - 1 ) );
}

function repayment( annuity, start_loan, interest, payment_number )
{
    return ( annuity - ( start_loan * interest ) ) * Math.pow( 1+interest, payment_number - 1 );
}