Lines Parallel to the Sides of a Triangle
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 .[more]
Drag the points A, B, or C to change the figure.[less]
The statement of the theorem is in "Notes on Euclidean Geometry" by Paul Yiu, p. 90.