1. Draw two circles with a diameter of 20 to make them tangent. 2. Make the common tangent of two circles from any point outside. The two common tangents are parallel, and one of them is AC direction as shown in the figure. 3. Constrain the tangents of the two circles to be horizontal, and the tangents of the two circles intersect with another point 4 at point A, as shown in the figure. Cut off the intersection with a common tangent that passes through two circles.