"why the fuck doesnt this work"
By GGMethos (https://pastebin.com/u/GGMethos)

URL: https://pastebin.com/X1cw0uXQ
Created on: Monday 28th of April 2014 09:50:33 PM CDT
Retrieved on: Monday 26 of October 2020 05:55:38 AM UTC


private void button3_Click(object sender, EventArgs e) //interest rate
{

if (textBox2.Text != "")
            {
                errorProvider1.SetError(textBox2, "Please keep this blank");
            }

if (Information.IsNumeric(textBox1.Text) && Information.IsNumeric(textBox3.Text) && Information.IsNumeric(textBox4.Text)) //makes sure the inputs are only numbers
            {
    double loanAmount3 = Convert.ToDouble(textBox1.Text);
    double numOfmon3 = Convert.ToDouble(textBox4.Text);
    double payment3 = Convert.ToDouble(textBox3.Text);

    double initial3 = (2 * (numOfmon3 * payment3 - loanAmount3) / (numOfmon3 * loanAmount3));
    double rOld3 = (initial3 * (Math.Pow((1 + initial3), numOfmon3)) / ((Math.Pow((1 + initial3), numOfmon3) - 1))) - (payment3 / loanAmount3);

    double b2 = payment3 * Math.Pow((1 + rOld3), -numOfmon3);
    double c2 = (rOld3 * loanAmount3);
    double num3 = payment3 - (b2 - c2);
    double denom3 = numOfmon3 * (payment3 * Math.Pow((1 + rOld3), (-numOfmon3 - 1)) - loanAmount3);
    bool terminate2 = false;

    double rNew2;


while (terminate2 == false)
			 { //terminating factor to exit the loop
				 rNew2 = rOld3 - (num3 / denom3);
				 if (Math.Abs(rNew2 - rOld3) >= 0.01) //loops until difference is less than .01, then terminates
				 {
					 rOld3 = rNew2;
					 
				 }
				 else
				 {
					 terminate2 = true;
				 }
textBox2.Text = rNew2.ToString(); //outputs desired results
				 }
				 }
				 //in case of user error (doesn't protect against user inputting non-numbers)
else
{
textBox2.Text = "PLEASE JUST USE NUMBERS";
}
}