
ZOJ Problem Set  1199
Given two circles on the same plane which are centered at (x1,y1) and (x2,y2) ,with radiuses r1 and r2, respectively.We can see that they have two common tangent lines in most of the cases.Now you are asked to write a programme to calculate the point of intersection of the two tangents if there exists one. ( See Figure 1 )
Figure. 1 Point of intersection
Output For each figure, you are supposed to output the coordinates (x, y) of the point
of intersection if it exists.The x and y must be rounded to two decimal places
and be separated by one space.If there is no such point exists simply output
"Impossible." 2 0 0 10 0 0 5 0 0 10 10 0 1
Impossible. 11.11 0.00 Notice The common tangent lines like the following figure don't take into account; Source: Zhejiang University Local Contest 2002, Preliminary 