2025 SSMO Speed Round Problems/Problem 4

Revision as of 15:38, 9 September 2025 by Sedro (talk | contribs) (Solution)

Problem

In rectangle $ABCD,$ let $AB = 8,BC = 15,\omega$ be the circumcircle of $ABCD$, $\ell$ be the line through $B$ parallel to $AC,$ and $X \neq B$ be the intersection of $\ell$ and $\omega$. Suppose the value of $BX$ can be expressed as $\frac{m}{n},$ where $m$ and $n$ are relatively prime positive integers. Find $m+n$.

Solution

import geometry;
unitsize(3cm);

point B=dir(aSin(0.47)); point C=dir(180-aSin(0.47)); point D=dir(180+aSin(0.47)); point A=dir(-aSin(0.47));
<br /> point X=

draw(A--B--C--D--cycle,p=black+0.3mm);
draw(unitcircle,p=blue+0.3mm);

dot(A,linewidth(4)); dot(B,linewidth(4)); dot(C,linewidth(4)); dot(D,linewidth(4));

label("$A$",A,dir(45));
label("$B$",B,dir(135));
label("$C$",C,dir(215));
label("$D$",D,dir(-45));
label("$\omega$",(0,-0.9));
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