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Geometry Difficulty 7.1 National olympiad, round 2 Find the answer

Let A1B1C1D1A_1B_1C_1D_1 be an arbitrary convex quadrilateral. PP is a point inside the quadrilateral such that each angle enclosed by one edge and one ray which starts at one vertex on that edge and passes through point PP is acute. We recursively define points Ak,Bk,Ck,DkA_k,B_k,C_k,D_k symmetric to PP with respect to lines Ak1Bk1,Bk1Ck1,Ck1Dk1,Dk1Ak1A_{k-1}B_{k-1}, B_{k-1}C_{k-1}, C_{k-1}D_{k-1},D_{k-1}A_{k-1} respectively for k2k\ge 2.
Consider the sequence of quadrilaterals AiBiCiDiA_iB_iC_iD_i.
i) Among the first 12 quadrilaterals, which are similar to the 1997th quadrilateral and which are not?
ii) Suppose the 1997th quadrilateral is cyclic. Among the first 12 quadrilaterals, which are cyclic and which are not?

A number or a short expression. Spacing and $ signs are ignored.

Solution

Let A1B1C1D1 A_1B_1C_1D_1 be an arbitrary convex quadrilateral. P P is a point inside the quadrilateral such that each angle enclosed by one edge and one ray which starts at one vertex on that edge and passes through point P P is acute. We recursively define points Ak,Bk,Ck,Dk A_k, B_k, C_k, D_k symmetric to P P with respect to lines Ak1Bk1,Bk1Ck1,Ck1Dk1,Dk1Ak1 A_{k-1}B_{k-1}, B_{k-1}C_{k-1}, C_{k-1}D_{k-1}, D_{k-1}A_{k-1} respectively for k2 k \ge 2 . Consider the sequence of quadrilaterals AiBiCiDi A_iB_iC_iD_i .

i) Among the first 12 quadrilaterals, the ones that are similar to the 1997th quadrilateral are the 1st, 5th, and 9th quadrilaterals.

ii) Suppose the 1997th quadrilateral is cyclic. Among the first 12 quadrilaterals, the ones that are cyclic are the 1st, 3rd, 5th, 7th, 9th, and 11th quadrilaterals.

The answer is:
1. 1,5,92. 1,3,5,7,9,11 \begin{aligned} &\text{1. } \boxed{1, 5, 9} \\ &\text{2. } \boxed{1, 3, 5, 7, 9, 11} \end{aligned}

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Source: Omni-MATH, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.