Russian Olympiad
by yugrey, Nov 26, 2014, 5:19 PM
http://www.artofproblemsolving.com/Forum/resources.php?c=143&cid=61&sid=3e5cd2771b87433faf693e2f9874f224
Nice problem source...
http://www.artofproblemsolving.com/Forum/resources.php?c=143&cid=61&year=2014&sid=3e5cd2771b87433faf693e2f9874f224
Grade 11...
Day 1:
#1
Nice problem source...
http://www.artofproblemsolving.com/Forum/resources.php?c=143&cid=61&year=2014&sid=3e5cd2771b87433faf693e2f9874f224
Grade 11...
Day 1:
#1
Say we have
as
ranges over positive reals, where
is a fixed positive real.
Say that
is irrational. In this case we can set
to be such that
,
. Ranging over all such
, we have
comes arbitrarily close to
so we can have
while
and
. No irrational solutions.
Say that
is rational. Then we have
and we can turn
into
.
So then assume we had
for all positive
where WLOG
. Then just set
and
, and ranging we have that
keeps incrementing by
of the circle. So we can increase it by multiples of
freely and then if
we can pick
which gives us a contradiction. So we have that
or
, and also
or
. Now, then
is
,
,
, or
. Note the
is just the
and the
and
cases are the same by symmetry.
It suffices to examine
and
.
Just pick
,
and done with the first one.
So it suffices to check if the second one is true. Note it is actually just the
case.
We wonder if
holds for all positive reals
. If we plug in
though, we have
is positive, but
whereas
, so oops. So no solutions exist.



Say that










Say that




So then assume we had























It suffices to examine


Just pick


So it suffices to check if the second one is true. Note it is actually just the

We wonder if





