70
Let three circles R1,R2,R3 ,with centers A1,A2,A3 and ridii r1,r2,r3 respectively be mutually tangent to each other externally. Suppose that the tangent to the circumcircle of the triangle A1A2A3 at A3 and the two external common tangents of R1 and R2 meet at a common point P , as shown in the figure below, Given that r1=18cm,r2=8cm,and r3=K cm, find the value of K
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