private void przeciecie_click(object sender, EventArgs e)
        {
            pictureBox1.Refresh();

            PointF p1 = new PointF(float.Parse(textBox1.Text.Replace('.', ',')), float.Parse(textBox2.Text.Replace('.', ',')));
            PointF p2 = new PointF(float.Parse(textBox3.Text.Replace('.', ',')), float.Parse(textBox4.Text.Replace('.', ',')));

            PointF p3 = new PointF(float.Parse(textBox5.Text.Replace('.', ',')), float.Parse(textBox6.Text.Replace('.', ',')));
            PointF p4 = new PointF(float.Parse(textBox7.Text.Replace('.', ',')), float.Parse(textBox8.Text.Replace('.', ',')));

            DrawLine(pen, p1, p2);
            DrawLine(pen, p3, p4);

            DrawPoint(pen3, p1);
            DrawPoint(pen3, p2);
            DrawPoint(pen3, p3);
            DrawPoint(pen3, p4);

            float delta = (p2.X - p1.X) * (p3.Y - p4.Y) - (p3.X - p4.X) * (p2.Y - p1.Y);

            if (delta != 0)
            {
                float deltaMi = (p3.X - p1.X) * (p3.Y - p4.Y) - (p3.X - p4.X) * (p3.Y - p1.Y);


                float mi = (deltaMi / delta);
                float x = (1 - mi) * p1.X + mi * p2.X;
                float y = (1 - mi) * p1.Y + mi * p2.Y;

                PointF cross = new PointF(x, y);

//                g.DrawLine(pen, cross, new PointF(400, 400));
                DrawPoint(pen2, cross);
            }

            textBox1.BackColor = Color.LightGreen;
            textBox2.BackColor = Color.LightGreen;
            textBox3.BackColor = Color.LightGreen;
            textBox4.BackColor = Color.LightGreen;

            textBox5.BackColor = Color.LightGreen;
            textBox6.BackColor = Color.LightGreen;
            textBox7.BackColor = Color.LightGreen;
            textBox8.BackColor = Color.LightGreen;
        }





 private void kat_click(object sender, EventArgs e)
        {
            pictureBox1.Refresh();
            PointF p0 = new PointF(0, 0);
            PointF p1o = new PointF(float.Parse(textBox1.Text.Replace('.', ',')), float.Parse(textBox2.Text.Replace('.', ',')));
            PointF p2o = new PointF(float.Parse(textBox3.Text.Replace('.', ',')), float.Parse(textBox4.Text.Replace('.', ',')));

            PointF p1 = new PointF(p1o.X / Len(p1o), p1o.Y / Len(p1o));
            PointF p2 = new PointF(p2o.X / Len(p2o), p2o.Y / Len(p2o));

            g.DrawLine(pen, p0, p1o);
            g.DrawLine(pen, p0, p2o);
            float alfa = (float) Math.Acos(Math.Abs(p1.X * p2.X + p1.Y * p2.Y));
            alfa = alfa / (float) Math.PI * 180;

            g.DrawString("Alfa = " + alfa, DefaultFont, new SolidBrush(Color.Black), 10, 375);

            textBox1.BackColor = Color.LightGreen;
            textBox2.BackColor = Color.LightGreen;
            textBox3.BackColor = Color.LightGreen;
            textBox4.BackColor = Color.LightGreen;

            textBox5.BackColor = Color.LightGray;
            textBox6.BackColor = Color.LightGray;
            textBox7.BackColor = Color.LightGray;
            textBox8.BackColor = Color.LightGray;
        }