Проблема в построении графика посредством Graphics

namespace Графики_ужас
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{

}





public double Result(float x2)
{
string form = textBox2.Text;
string[] opand = form.Split('+', '-', '*', '/', '^');
string[] opats = form.Split('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'x');
for (int i = 0; i < opand.Length; i++)
{
if (opand[i] == "x")
{
opand[i] = Convert.ToString(Convert.ToInt32(x2));
}
}
int[] opandp = opand.Select(s => int.Parse(s)).ToArray();
double resulted = 0;
switch (opats[0])
{
case "*": resulted = opandp[0] * opandp[1]; break;
case "/": resulted = opandp[0] / opandp[1]; break;
case "^": resulted = Math.Pow(Convert.ToDouble(opandp[0]), Convert.ToDouble(opandp[1])); break;
}
return resulted;
}

private void button2_Click(object sender, EventArgs e)
{
Graphics graphs = pictureBox2.CreateGraphics();
Pen myPen = new Pen(Color.Black, Width = 3);
int numInt = 100;
float xmin = 0, xmax = 2, ymin = 0, ymax = 4;
float xstep = (xmax - xmin) / numInt;
float kx = pictureBox2.Width / xmax, ky = pictureBox2.Height / ymax;
float x1 = xmin, y1 = x1 * x1, x2, y2;
for (int i = 0; i < numInt; i++)
{
x2 = x1 + xstep;
y2 = Convert.ToSingle(Result(x2));
graphs.DrawLine(myPen, kx * x1, pictureBox2.Height - ky * y1, kx * x2, pictureBox2.Height - ky * y2);
x1 = x2;
y1 = y2;
}

}
}
}