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.
such that![\[f(x+yf(x))+f(xf(y)-y)=f(x)-f(y)+2xy\]](http://latex.artofproblemsolving.com/e/b/c/ebccae7e765d9fc3c8605e58a7399a70127b39b1.png)
(use in a problem for junior) to practice. Can anyone share to me?
+1 w
, such that 
Prove that :
equality cases : ?
distinct positive integers such that adding the product of any two of them to 
yields a perfect square?
be a sequence of positive integers with 
, 
and![\[a_n = a_{n-1}^{a_{n-1}a_{n-2}}-1\]](http://latex.artofproblemsolving.com/1/b/f/1bf1a88979e7d2b33530de979d66a4e81032953d.png)
for all 
. Show that if 
is a prime less than 
for some positive integer 
, then there exists 
such that 
.
be a triangle with circumcircle 
, incentre 
. The second intersections of 
, 
, and 
with are 
, 
, and 
, respectively. Lines and 
intersect at 
and lines 
and 
intersect at 
. Suppose 
and 
intersect again at 
. Lines 
and 
intersect the circumcircle of triangle 
again at 
and 
, respectively.
lies on 
.
for which
be an acute angled scalene triangle with circumcircle 
. Let 
and 
be the circumcenter and orthocenter of 
respectively. Let 
and 
be points on segments 
and , respectively, such that
Prove that 
and 
intersect on the circumcircle of 
.
grid with 
rows and 
columns, and each square of the grid is filled with a non-negative integer. Let 
be the average of all the numbers in the grid. Prove that if 
the there exist two identical rows (meaning same numbers in the same order).
is called feirense if it is possible to write on a sheet of paper some integers such that every positive divisor of less than is the difference between two numbers on the sheet, and no other positive number is.
be a square with 
side length and with center 
. A rhombus 
is drawn where point 
lies on line 
. What is the area of ?
and 
be midpoints of and 
. Let 
be perpendicular to and 
be perpendicular to . we have 
and we want to prove 
. Note that 
and 
is cyclic so 
is cyclic. Now Note that 
and 
so 
and 
are similar and 
as wanted.
and 
.
,
be midpoints of segments (respectively) 
.
are orthogonal projections of points 
lines 
as a radius. 
area of triangles 
is equal. Hence 
.
.