Tangent of two circles.

Question

I am trying to write code that will draw a line that is tangent between two circles. so far I could draw several circles and lines between the centers.
I have a class that stores the values ​​used when drawing circles (radius, position). I need a method in this class to find all possible tangent points between two circles.
any help would be great.
this is what I still have (it could very well be garbage)

public static Vector2[] Tangents(circle c1, circle c2)
{
            if (c2.radius > c1.radius)
            {
                circle temp = c1;
                c1 = c2;
                c2 = temp;
            }
            circle c0 = new circle(c1.radius - c2.radius, c1.center);
            Vector2[] tans = new Vector2[2];
            Vector2 dir = _point - _center;
            float len = (float)Math.Sqrt((dir.X * dir.X) + (dir.Y * dir.Y));
            float angle = (float)Math.Atan2(dir.X, dir.Y);
            float tan_length = (float)Math.Sqrt((len * len) - (_radius * _radius));
            float tan_angle = (float)Math.Asin(_radius / len);
            tans[0] = new Vector2((float)Math.Cos(angle + tan_angle), (float)Math.Sin(angle + tan_angle));
            tans[1] = new Vector2((float)Math.Cos(angle - tan_angle), (float)Math.Sin(angle - tan_angle));
            Vector2 dir0 = c0.center - tans[0];
            Vector2 dir1 = c0.center - tans[1];

            Vector2 tan00 = Vector2.Add(Vector2.Multiply(tans[0], (float)c2.radius), c1.center);
            Vector2 tan01 = c2.center;
            Vector2 tan10 = Vector2.Add(Vector2.Multiply(tans[1], (float)c2.radius), c1.center);
            Vector2 tan11 = c2.center;
}

Answer 1

, . Mathworld .

EDIT: .