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MathNet 1987 — Part 01 Question 17

Math Olympiad Vault · MathNet 1987 — Part 01

Question 17

In an acute triangle $ABC$ the inner bisector of the angle $A$ cuts to $BC$ at $L$ and cuts the circumscribed circumference of $ABC$ again on $N$. We draw perpendiculars from $L$ to $AB$ and $AC$, with feet $K$ and $M$, respectively. Prove that the quadrilateral $AKNM$ and triangle $ABC$ have the same area.