How to rotate an object according to the cursor position ? ( C# )

Here is my problem, i have a triangle in the middle on my screen, i want it to rotate following my cursor with the top of the triangle. I got my cursor position in a World Scale with ScreenToWorldPoint. Here is the script I wrote.

 void Update () {
         v3 = Input.mousePosition;
         v3.z = -10;
         v3 = Camera.main.ScreenToWorldPoint(v3);
         cursor_x = v3.x;
         cursor_y = v3.y;
         if (cursor_x < 0)
         {
             position_x = -1;
         }else
         {
             position_x = 1;
         }
         if (cursor_y < 0)
         {
             position_y = -1;
         }else
         {
             position_y = 1;
         }
         if (position_x == -1 && position_y==-1)
         {
             tan = cursor_y / cursor_x;
             angle =(Mathf.Atan(tan) * Mathf.Rad2Deg);
             this.GetComponent<Rigidbody2D>().transform.Rotate(0f, 0f, -90 - angle, Space.World); //= Quaternion.Euler(0f, 0f, -90-angle);
         }
         else if(position_x==1 && position_y==-1)
         {
             tan = cursor_y / cursor_x;
             angle = (Mathf.Atan(tan) * Mathf.Rad2Deg);
             this.GetComponent<Rigidbody2D>().transform.Rotate(0f, 0f, 90 + angle, Space.World); //= Quaternion.Euler(0f, 0f, 90+angle);
         }
         else if (position_x == -1 && position_y == 1)
         {
             tan = cursor_x / cursor_y;
             angle = (Mathf.Atan(tan) * Mathf.Rad2Deg);
             this.GetComponent<Rigidbody2D>().transform.Rotate(0f, 0f, - angle, Space.World); //= Quaternion.Euler(0f, 0f, -angle);
         }
         else if (position_x == 1 && position_y == 1)
         {
             tan = cursor_x / cursor_y;
             angle = (Mathf.Atan(tan) * Mathf.Rad2Deg);
             this.GetComponent<Rigidbody2D>().transform.Rotate(0f, 0f, angle, Space.World); //= Quaternion.Euler(0f, 0f, angle);
         }