[/quote]
,
and 
then prove 
be the set of positive real numbers.
such that there exists a function 
with the property:![\[
f(y^2f(x) + y + c) = xf(x+y^2)
\]](http://latex.artofproblemsolving.com/e/3/0/e30ee6d9f69cc43422a5c2b9813192a632d359cb.png)
for all 
.
be non-negative real numbers such that 
Prove that
and 
.
,![\[ a^{b+c} b^{c+a} c^{a+b} \leq 1 . \]](http://latex.artofproblemsolving.com/0/c/e/0ce097b0b507403c959c2992cae1217ecdd7e581.png)
be a finite sequence of positive integers. Prove that there exist nonnegative integers 
and 
such that 
holds for all integers 
be a positive integer. Dominoes are placed on a 
board in such a way that every cell of the board is adjacent to exactly one cell covered by a domino. For each 
or 
.
of positive real numbers that satisfy the system:![\[
\begin{aligned}
11bc - 36b - 15c &= abc \\
12ca - 10c - 28a &= abc \\
13ab - 21a - 6b &= abc.
\end{aligned}
\]](http://latex.artofproblemsolving.com/1/7/0/170e1cfaee90f5c37428fa75192ac889261a8f83.png)
be positive reals. Prove that there is a cyclic permutation 
of 
such that the inequality:![\[
\frac{a}{xa + yb + zc} + \frac{b}{xb + yc + za} + \frac{c}{xc + ya + zb} \geq \frac{3}{x + y + z}
\]](http://latex.artofproblemsolving.com/5/5/3/553527fc40a1b7d29dbdfb4b5e63635308f46c85.png)
and 
.
,
,
.
with diameter 
,
at a point 
.
meets line 
at 
.
and 
intersect at a point 
on 
.
Prove that: 
is the sum of 
square numbers
Let 
and 
is the sum of 
is the sum of 
and incenter 
and let 
,
,
are selected on sides 
,
such that 
,
,
.
intersects 
other than 
and 
meet on 
Y by rcorreaa, Adventure10
Let 
be an acute-angled triangle with circumcenter 
and orthocenter 
. The circle with center 
passes in the points 
and and is tangent to the circumcircle of . Define 
analogously, let 
the symmetric of to the sides 
and 
, respectively. Prove that the lines 
are concurrents.
be an acute-angled triangle with circumcenter 
and orthocenter 
. The circle with center 
passes in the points 
and and is tangent to the circumcircle of . Define 
analogously, let 
the symmetric of to the sides 
and 
, respectively. Prove that the lines 
are concurrents.
with circumcircle 
,
at 
.
and 
cuts 
.
are defined at the same with 
,
are concurrent.
,
is the circumcenter of 
and let 
cuts 
again at 
.
are collinear. We also can prove that 
are cyclic. So 
pass through the circumcenter of 
.
as 
are the circumcenters of 
and thus the points 
lie on the perpendicular bisector of 
and so we have our desired result by Ceva's theorem.
