Line tangent to circle

[MahaB82A]

I wish to make line tangent to two circles. Purple color shows path of the circle. It also shows intersect. What does this mean?

Is there any tool to make line tangent to both circles?

Line tangent to circle  

[Monika Gause]

There is the script Common tangents and there is a (not for free) plugin SubScribe that can do this: 

The script:

http://shspage.com/aijs/en/#common