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.
, are there infinitely many positive integers 
such that 
is a perfect square? (Here 
denotes the integer part of the real number 
?
be an acute triangle with 
, Let 
be the intouch triangle with 
,
,
,, let 
be the intersecttion of the perpendicular from 
to 
with 
, and 
.
and 
are concylic
the set 
can be partitioned into 
triples in such a way that the numbers from each triple are the lengths of the sides of some obtuse triangle. be a triangle with circumcircle 
, circumcenter 
, and orthocenter 
. Assume that 
and that 
. Let 
and 
be the midpoints of sides and 
, respectively, and let 
and 
be the feet of the altitudes from 
and 
in 
, respectively. Let 
be the intersection of line 
with the tangent line to at 
. Let 
be the intersection point, other than , of with the circumcircle of 
. Let 
be the intersection of lines 
and . Prove that 
.
be the foot of perpendicular from to the Euler line (the line passing through the circumcentre and the orthocentre) of an acute scalene triangle . A circle 
with centre 
passes through and , and it intersects sides and at and 
respectively. Let be the foot of altitude from to 
, and let be the midpoint of . Prove that the circumcentre of triangle 
is equidistant from and .
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 
.
and 
be 2 distinct positive integers.
be in an integer. Prove why ?
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 
.
.
with maximums 
and 
. If 
, and 
can be expressed as 
where is a positive integer, find .
and 
. Prove that
Let and 
. Prove that
Let and 
. Prove that
Let and 
. Prove that
that fulfills the following two properties: 
is periodic of period 
(that is, for all 
, 
), and by restricting to the interval ![$[-2,3]$](http://latex.artofproblemsolving.com/c/0/e/c0e1b59587281eead4f0941cda7da6a32a663e3f.png)
, coincides to 
. Determine the value of 
![$f(x)=x^2\forall x\in[-2,3]$](http://latex.artofproblemsolving.com/1/4/1/141a4dee7ae1dd72ae47c0af86a74597ca1b110c.png)
.
,
.