MathDB
2018-2019 Fall OMO Problem 30

Source:

November 7, 2018

Problem Statement

Let ABCABC be an acute triangle with cosB=13,cosC=14\cos B =\frac{1}{3}, \cos C =\frac{1}{4}, and circumradius 7272. Let ABCABC have circumcenter OO, symmedian point KK, and nine-point center NN. Consider all non-degenerate hyperbolas H\mathcal H with perpendicular asymptotes passing through A,B,CA,B,C. Of these H\mathcal H, exactly one has the property that there exists a point PHP\in \mathcal H such that NPNP is tangent to H\mathcal H and POKP\in OK. Let NN' be the reflection of NN over BCBC. If AKAK meets PNPN' at QQ, then the length of PQPQ can be expressed in the form a+bca+b\sqrt{c}, where a,b,ca,b,c are positive integers such that cc is not divisible by the square of any prime. Compute 100a+b+c100a+b+c.
Proposed by Vincent Huang