drawing y=sin(θ)*cos(θ) in c# with pen : i want draw sin(θ)*cos(θ)  but don't work 
i cant draw sin or  cos 
but i want draw sin(θ)*cos(θ) together

here is my code 

         private void button1_Click(object sender, EventArgs e)
        {
            Graphics drw = this.CreateGraphics();
            Pen pen = new Pen(Brushes.Black, 7.0f);
            float x1 = 0;
            float y1 = 0;
            float xoy = 200;
            float ef = 20;

            for (double  i=0;i<40;i+=1)
            {
                 double radi = (float)(i * 180 / Math.PI);
              
                float temp = (float)Math.Cos(radi)*(float)Math.Sin(radi);
               
                drw.DrawLine(pen, x1 * ef, y1 * ef + xoy, ef * (float)i, temp * ef + xoy);
                x1 = (float)i;
                y1 = temp;


            }


and i want this result 

[result i want][1]
  [1]: https://i.stack.imgur.com/JLQbA.jpg