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Please help ! My idea:

Let's say we we have two circles : (x1, y1, r1) and (x2, y2, r2), and have to find one of the tangents. Let's say that r1+r2 < dist( (x1,y1), (x2,y2) )

We start with two different circles : (0,r1, r1) and (a, r2, r2), where is such that dist( (0,r1), (a,r2) ) = dist( (x1,y1 ...