MathDB
Tangent geometry

Source: 2006 AIME II 9

March 28, 2006
geometryanalytic geometrygraphing linessloperatiosimilar trianglesAMC

Problem Statement

Circles C1\mathcal{C}_1, C2\mathcal{C}_2, and C3\mathcal{C}_3 have their centers at (0,0), (12,0), and (24,0), and have radii 1, 2, and 4, respectively. Line t1t_1 is a common internal tangent to C1\mathcal{C}_1 and C2\mathcal{C}_2 and has a positive slope, and line t2t_2 is a common internal tangent to C2\mathcal{C}_2 and C3\mathcal{C}_3 and has a negative slope. Given that lines t1t_1 and t2t_2 intersect at (x,y)(x,y), and that x=pqrx=p-q\sqrt{r}, where pp, qq, and rr are positive integers and rr is not divisible by the square of any prime, find p+q+rp+q+r.