Angle Bisector for an Angle Subtended by a Tangent Line

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Let a circle be internally tangent to another circle at the point A. Draw a tangent line through a point C on the inner circle and let D and B be its points of intersection with the outer circle. Then AC bisects DAB.
Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA
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"Angle Bisector for an Angle Subtended by a Tangent Line"
http://demonstrations.wolfram.com/AngleBisectorForAnAngleSubtendedByATangentLine/
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Published: March 7 2011