Let triangle have incircle , which touches , and at , and , respectively. Then, let and be circles tangent to and internally tangent to at and , respectively. Let be the intersection of line and the line passing through the centers of and . If and have radii 5 and 6, respectively, compute .
Solution
Let the centers of and be and . Let intersect again at , and let intersect again at . Note that since and must be tangent to at the same point (by equal tangents), so must be the radical axis of and , so is cyclic. Thus, we have Thus, we have is tangent to , and similarly it must be tangent to as well. Now, note that by Monge's theorem on , and , we have that must be the intersection of the external tangents of and . Since is an external tangent, we have , and are collinear. Thus, by power of a point, we have . Note that and . Thus, we have .
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