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Re: Geometry Marathon : Season 3

Posted: Fri Dec 29, 2017 12:45 pm
by joydip
joydip wrote:
Thu Dec 14, 2017 5:57 pm
Lemma 5: Let $F_e$ be the feuerbach point of $\triangle ABC$. Then $F_e , A_o$ and $L_a$ are colinear .
Better proof : $F_e , A_o$ and $L_a$ are the pairwise center of similitudes of the incircle , ninepoint circle and the $A$-excircle . So by d'Alembert's Theorem $F_e , A_o$ and $L_a$ are colinear .