A Theorem about Two Tangent Circles

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Let A and C be the centers of two tangent circles. Draw a line from a point E through the intersection of the two circles and let that line intersect the circles at B and D. Then AB is parallel to CD.
Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA
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For more information see Two Touching Circles.
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"A Theorem about Two Tangent Circles"
http://demonstrations.wolfram.com/ATheoremAboutTwoTangentCircles/
Wolfram Demonstrations Project
Published: March 7 2011