Finding the Radius for an Inserted Circle 笛卡尔定理 - 2017 ACM-ICPC 亚洲区（南宁赛区）网络赛
Three circles C_{a}Ca, C_{b}Cb, and C_{c}Cc, all with radius RR and tangent to each other, are located in two-dimensional space as shown in Figure 11. A smaller circle C_{1}C1 with
