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.
is a cyclic quadrilateral inscribed in a circle of radius one unit. If 
, prove that is a square.
, 
, 
, 
satisfy 
and 
. Prove that there exists a permutation 
of 
such that 
.
be a cyclic quadrilateral. A circle centered at 
passes through 
and 
and meets lines 
and 
again at points 
and 
(distinct from 
). Let 
denote the orthocenter of triangle 
Prove that if lines 
are concurrent, then triangle 
and 
are similar.
such that 
, where 
are non-negative reals such that 
.
.
a tangencial quadrilateral that is not a rhombus, let 
be lengths of tangents from 
to the incircle of the quadrilateral which center is 
. Let 
be the midpoints of 
resp. Prove that![\[ \frac{MI}{IN}=\frac{a+c}{b+d} \]](http://latex.artofproblemsolving.com/e/7/0/e709acb8b17c0466a385ba8e7a89bb1bf16c72af.png)
is given. It turns out that for every positive integer number 
, for which the numbers 
and 
are positive, they have the same number of divisors. Is it necessarily true that 
?
with as its incenter. Let be the intersection of 
and and define 
in a similar way. Furthermore, let 
. Prove that if 
, then 
are concyclic.
positive integers. Product of any one of them with sum of remaining numbers increased by 
is divisible with sum of all numbers. Prove that sum of squares of all numbers is divisible with sum of all numbers
![$P \in \mathbb R[x,y]$](http://latex.artofproblemsolving.com/8/a/0/8a0576299e976c51607959fb68c7c742b2a49c6a.png)
with ![$P \not\in \mathbb R[x] \cup \mathbb R[y]$](http://latex.artofproblemsolving.com/a/f/7/af71ba8c643d5bd8a2928fa6714ccd91713bd641.png)
and 
homeomorphismes of 
, 
is an homoemorphisme too.
is inscribed in a circle centered at , and 
. Let 
be the second intersection point of the circumcircles of the triangles 
and 
.
, and are collinear.
and 
are the circumcenters of the triangles , and , respectively, prove that the points 
are concyclic.
where is a positive integer and 
is a prime.(Don't get mad at me,I've used the search function and did not see a correct and complete solution anywhere.)
![\[
2^a + 3^b + 1 = 6^c
\]](http://latex.artofproblemsolving.com/1/9/e/19eb5efa2ccdf54cd277339f8d3b99f75168779d.png)
. Prove that if![\[\dfrac {1} {0^2+1}+\dfrac{1}{1^2+1}+\cdots+\dfrac{1}{(p-1)^2+1}=\dfrac{m} {n},\]](http://latex.artofproblemsolving.com/d/5/f/d5f55cc86a95d51109ace2dc3e737bddecc144b0.png)
(and the fraction 
is in reduced terms) then 
.
and 
(it is essential that 
is a quadratic residue modulo 
such that 
.
,![\[(p-1)! = \left (\prod_{\ell=1}^{(p-1)/2} \ell\right )\left (\prod_{\ell=1}^{(p-1)/2} (p-\ell)\right ) \equiv (-1)^{\frac {p-1} {2}}(((p-1)/2)!)^2 \pmod{p},\]](http://latex.artofproblemsolving.com/7/1/7/7174f97c5aeae035b4d7b4995a6f0c1fe9fe5b38.png)
.
we will have 
(although knowing the exact value is irrelevant in the sequel).
for 
(and it divides 
and 
)
;
yields 
,
.![\[E=\sum_{\ell\neq \pm \textrm{i}} \dfrac {1} {\ell^2 + 1} = \sum_{\ell\neq \pm \textrm{i}} \dfrac {1} {(\ell - \textrm{i})(\ell + \textrm{i})} = \dfrac {1} {2\textrm{i}} \sum_{\ell\neq \pm \textrm{i}} \left (\dfrac {1} {\ell - \textrm{i}} - \dfrac {1} {\ell + \textrm{i}}\right ).\]](http://latex.artofproblemsolving.com/1/d/f/1df3809beb7b98cf17abb6cd0497275473cd9d19.png)
.
,
,