Maths Olympiad Prep

Library / /31 of 155

Geometry Difficulty 5.3 AIME, harder Prove it Saudi Arabia

Let ABCABC be an acute, non-isosceles triangle which is inscribed in a circle (O)(O). A point II belongs to the segment BCBC. Denote by HH and KK the projections of II on ABAB and ACAC, respectively. Suppose that the line HKHK intersects (O)(O) at M,NM, N (HH is between M,KM, K and KK is between H,NH, N). Prove the following assertions:

1. If AA is the center of the circle (IMN)(IMN), then BCBC is tangent to (IMN)(IMN).
2. If II is the midpoint of BCBC, then BCBC is equal to 4 times the distance between the centers of two circles (ABK)(ABK) and (ACH)(ACH).

Solution

See the solution to Problem 1 in the test of level 4+. \square

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: MathNet, licensed CC-BY-4.0. Statement and solution reproduced as published; topic and difficulty added by this site.