# A Weird Cut Of Concentric Circles

Geometry Level 3

In the figure above, the circles are concentric with centre $$O$$. $$B$$ is a point on the larger circle. $$D$$ is a point on the smaller circle. $$BD$$ is joined, provided that $$BD$$ touches the circle at only one point. Now $$OB$$ is joined and extended to meet the larger circle at $$A$$. Find the distance between points $$A$$ and $$D$$ if the radii of the circles are $$4\sqrt{13}$$ and $$8$$ units respectively.

Clarification: Concentric circles are circles with a common centre.

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