//Ввод коэффициентов
        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            A = Convert.ToInt32(textBox1.Text.Trim());
        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {
            B = Convert.ToInt32(textBox2.Text.Trim());
        }

        private void textBox3_TextChanged(object sender, EventArgs e)
        {
            C = Convert.ToInt32(textBox3.Text.Trim());
        }