private void pictureBoxGraph_Click(object sender, EventArgs e)
 {
     if (chbPolynomial.Checked)
     {
         MouseEventArgs me = (MouseEventArgs)e;
         PointF         p  = graphDrawer.GetMouseLocation(me.Location, false);
         graphDrawer.AddPolynomialPoint(p.X, p.Y);
     }
 }