private void button1_Click(object sender, EventArgs e)
a = double.Parse(textBox1.Text);
b = double.Parse(textBox2.Text);
c = double.Parse(textBox3.Text);
S = Math.Sqrt(p * (p - a) * (p - b) * (p - c));
if (radioButton1.Checked)
textBox4.Text = S.ToString();
if (radioButton2.Checked)
textBox4.Text = P.ToString();