AoPS Academy
[/quote]
, do not answer with "
is a solution" only. Either you post any kind of proof or at least something unexpected (like "
is the smallest solution). Someone that does not see that is a solution of the above without your post is completely wrong here, this is an IMO-level forum.
with 
. Denote the orthocenter of 
as 
, the intersection of 
and 
as 
. Compute the length of 
.
be an acute triangle with orthocenter . Let 
, 
and 
be the feet of the altitudes of triangle opposite to vertices 
, 
, and 
respectively. Let 
and 
be the midpoints of 
and 
, respectively. Let 
be the intersection of lines 
and 
. Prove that is the circumcenter of triangle if and only if is the midpoint of 
.
and 
be two prime numbers, with being a divisor of 
. Prove that there exist integers 
such that the polynomial 
is divisible by the polynomial 
with 
is a multiple of and 
.
be the circumcircle of acute triangle . Points 
and 
are on segments 
and respectively such that 
. The perpendicular bisectors of 
and 
intersect minor arcs and of at points 
and 
respectively. Prove that lines 
and 
are either parallel or they are the same line. be a scalene acute triangle with incenter 
and circumcircle 
. 
is the midpoint of small arc 
on and 
is the projection of onto the line passing through the midpoints of and . A circle 
with center 
is internally tangent to at , and touches segment . If the circle with diameter 
meets again at 
, prove that 
bisects 
. be circumscribed about circle 
, and let be the orthocenter of 
. The circle touches line at . The tangent to the circle at meets at 
. Let be the midpoint of 
, and let the line 
meet again at 
. The tangent to parallel to meets the line 
at 
. Prove that 
is tangent to .
be two nonzero real numbers such that 
Consider the functions 
and 
satisfying the condition ![$$g(f(x+by))=a[f(x)+2yg(x)]+2xg(y)+bg(y)[y+g(y)],\quad\forall x,y\in\mathbb{R}.$$](http://latex.artofproblemsolving.com/3/c/9/3c974cb76aae7f529dcd85202b0c7d441a07d002.png)
(a) Prove that there exists a real number such that 
(b) Find all functions 
and 
that satisfy the given condition.
be a square and a point lies on the interior of such that triangle 
is equilateral. Evaluate 
to 
(inclusive) are selected randomly without repetitions, then either all of them will be odd, or all will be divisible by 
, or all will be divisible by 
of the sides enclosing the right angle equals 
while the length of the altitude 
on the hypotenuse is 
. Determine the length of the hypotenuse.
![\[
\frac{2a^2}{(b-c)^2} + \frac{2b^2}{(a-c)^2} + \frac{2c^2}{(b-a)^2} \geq 2 + \sum \left| \frac{(a+b-c)(b+c-a)}{(c-a)^2} \right|
\]](http://latex.artofproblemsolving.com/4/8/1/4813b0f718b56d880792297a5fe6141ad2e1f2ab.png)
and 
Prove that
, such that 
Prove that :
equality cases : ?
and 
.
