Four Concurrent Lines in a Cyclic Quadrilateral

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A cyclic quadrilateral has all four of its vertices on a circle.
Through the midpoint of each side of a cyclic quadrilateral draw a line perpendicular to the opposite side or its extension. The four resulting lines are concurrent.
Drag the purple points to change the figure.

Details

A. Bogomolny, "Four Concurrent Lines in a Cyclic Quadrilateral," Interactive Mathematics Miscellany and Puzzles.

External Links

Concurrent (Wolfram MathWorld)
Cyclic Quadrilateral (Wolfram MathWorld)

Permanent Citation

Jay Warendorff, Alexander Bogomolny
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​"Four Concurrent Lines in a Cyclic Quadrilateral"​
​http://demonstrations.wolfram.com/FourConcurrentLinesInACyclicQuadrilateral/​
​Wolfram Demonstrations Project​
​Published: March 7, 2011