Lines Parallel to the Sides of a Triangle

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Let ABC be a triangle and let the angle bisectors at A, B, and C intersect the opposite sides at points P, Q, and R. Draw lines from P, Q, and R parallel to AB, BC, and AC that intersect AC, AB, and BC at P', Q', and R'. Then .


Drag the points A, B, or C to change the figure.


Contributed by: Jay Warendorff (March 2011)
After work by: Paul Yiu
Open content licensed under CC BY-NC-SA



The statement of the theorem is in "Notes on Euclidean Geometry" by Paul Yiu, p. 90.

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