In triangle $ABC$, $\angle{BAC}=60^\circ$ and the incircle of $ABC$ touches $AB$ and $AC$ at $P$ and $Q$, respectively. Lines $PC$ and $QB$ intersect at $G$. Let $R$ be the circumradius of $BGC$. Find the minimum value of $R/BC$. Author: Alex Song
2011 Canadian Students Math Olympiad
For a fixed positive integer $k$, prove that there exist infinitely many primes $p$ such that there is an integer $w$, where $w^2-1$ is not divisible by $p$, and the order of $w$ in modulus $p$ is the same as the order of $w$ in modulus $p^k$. Author: James Rickards
Find the largest $C \in \mathbb{R}$ such that \[\frac{x+z}{(x-z)^2} +\frac{x+w}{(x-w)^2} +\frac{y+z}{(y-z)^2}+\frac{y+w}{(y-w)^2} + \sum_{cyc} \frac{1}{x} \ge \frac{C}{x+y+z+w}\] where $x,y,z,w \in \mathbb{R^+}$. Author: Hunter Spink
Circles $\Gamma_1$ and $\Gamma_2$ have centers $O_1$ and $O_2$ and intersect at $P$ and $Q$. A line through $P$ intersects $\Gamma_1$ and $\Gamma_2$ at $A$ and $B$, respectively, such that $AB$ is not perpendicular to $PQ$. Let $X$ be the point on $PQ$ such that $XA=XB$ and let $Y$ be the point within $AO_1 O_2 B$ such that $AYO_1$ and $BYO_2$ are similar. Prove that $2\angle{O_1 AY}=\angle{AXB}$. Author: Matthew Brennan