The only thing we really have to work with are the radii of the circles. I believe that using each radius, we can figure out things about angles.
Hopefully I'll have time to work on it later.
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A common tangent touches the 1st circle at point C and the second at point D.
Does this mean that the line is tangent to both circles? If that's the case, then I think there are only two possible places for such a line. Either tangent to the very top, or very bottom.
Edit: nevermind, I made the assumption that the circles were the same size.
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