viernes, 23 de marzo de 2012

Three Parallel Segments

This is based on an idea of Juan Bosco Romero: Let $ABC$ be a triangle with incenter $I$ and circumcenter $O$.
Call $A_b, A_c$ the reflection of $A$ on lines $BI$ and $CI$, respectively. Define $B_c, B_a$ and $C_a, C_b$ analogously.
Then line segments $B_cC_b$, $C_aA_c$ and $A_bB_c$ are parallel. They are also proportional to the sides of $ABC$ and we have the ratios $B_cC_b/BC = C_aA_c/CA = A_bB_a/AB = OI/R$.

The common infinite point of lines $B_cC_b, C_aA_c$ and $A_bB_c$ is the isogonal conjugate of the point $X_{100}$.

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