Art of Random Solving
by SomeonecoolLovesMaths, Jan 27, 2025, 10:29 PM
Here are a few of my random solves:
My Solution
My Solution
My Solution
My Solution
Solution
Solution
Solution
Solution
Quote:
In a grid of unit squares, a
is defined as a pair of unit squares which share a vertex but do not share a side. For which pairs of integers
can an
rectangular grid of unit squares be tiled with cucumbers?



My Solution
Claim: We can fill all
rectangles iff
.
Proof: First let us show that it is possible for
. Say the rectangle has
rows and
columns. Ofcourse
. So keeping
fixed, we induct on
. We divide the triangle into a
rectangle and
rectangle. By induction both can be filled using cucumbers and so can the whole rectangle. For the base case of
, just divide the triangle into
many
squares, which is possible since
is even too! 
Now a much simpler case is the one where both
are odd. So there are
squares. Each cucumber will fill
squares and hence it cannot fill odd number of squares and hence we are done! 
Now the case where
is even and
is odd (or vice versa). Wolog assume there are
rows and
columns (or just rotate the square by
. Next number the columns
. Colour the odd columns red and the even columns blue. Note, there is one more column of red than blue. Thus number of red squares
number of blue squares. Each cucumber must occupy atleast one red and one blue square. Thus if the board is tiled using cucumbers then we get that number of red tiles
number of blue tiles. A contradiction! 
Hence only
will work.


Proof: First let us show that it is possible for













Now a much simpler case is the one where both




Now the case where









Hence only

Quote:
Determine all finite nonempty sets
of positive integers satisfying
is an element of
for all
and
(not necesarily distinct in S)





My Solution
Let
.
Claim:
is always in the set.
Proof: Take
which gives
is in the set
. 
Claim:
does not have any odd numbers.
Proof: FTSOC assume the contrary. Let
be the largest odd number in the set. Then
is in
, is odd, and is greater than
, contradiction!
Claim: There is no even number greater than
in
.
Proof: Say there exists an
such that
and is the least even element in the set after
.
Claim:
.
Proof:
which is our original claim. 
But then either
is even
(or else
) which is a contradiction, or it is odd which then eventually leads to contradiction. Hence
is the only possibility and hence
. 

Claim:

Proof: Take




Claim:

Proof: FTSOC assume the contrary. Let




Claim: There is no even number greater than


Proof: Say there exists an



Claim:

Proof:


But then either






Quote:
The numbers
and
are prime and satisfy
for some positive integer
. Find all possible values of
.


![\[\frac{p}{{p + 1}} + \frac{{q + 1}}{q} = \frac{{2n}}{{n + 2}}\]](http://latex.artofproblemsolving.com/7/3/5/735ec9416a654f40121021bdd1233ffa86e42495.png)


My Solution
From the following equations we get, 
Ofcourse
And expanding gives
Ofcourse 
Since
and
so
.
Thus
can be
.
Thus
can be
.
Not diffucult to check that
work.









Thus


Thus


Not diffucult to check that

Quote:
Let
be a sequence of primes such that
and for
is the largest prime factor of
. Prove that
for any
.






My Solution
Note
,
,
. Say
such that
has its largest prime divisor as
. Thus
has to be of the form
. As
, thus
. Obviously by checking
. Thus
thus
. Thus
for some
, or,
. Now,
But
, contradiction! (Here
denotes the largest expononent of
in
).





















ISL 1977 wrote:
Let
be two natural numbers. When we divide
by
, we the the remainder
and the quotient
Determine all pairs
for which 







Solution
By division algorithm,
.
If
then the maximum value of
will be
. Thus
.
Thus
. 
. By Jacobi's two square theorem,
.

If




Thus




Quote:
Find the greatest possible value of
.

Solution
Because by Cauchy,
Thus, 


Quote:
For how many value of
the
is a perfect square number.


Solution
Checking mod
gives us,
. Hence
is obviously even.
Now,
.
Thus,
is a perfect square too!
As
is even, let
.
Let
.
Thus,
.
As
and
is a prime so,
and
.
Solving these two equations gives us that
and
.
Hence the only
which will work is
.



Now,

Thus,

As


Let

Thus,

As




Solving these two equations gives us that


Hence the only


Quote:
Find all
natural numbers such that for each of them there exist
primes such that these terms satisfy.

and
are primes.







Solution
Say
.
Observe
. Hence
.
Hence
. As
and
is a prime hence
. Thus
.
This means that
. Contradiction!
Hence
and
.
Thus,
and
are both primes.
which means that
has to be odd.
Case 1.
.
This can be easily ruled out by considering the expressions

Case 2.
Firstly, we consider the expressions
.Note that 
If
or
, we arrive at a contradiction. Hence,the only possibility left is
.
Since
.
Consider the expressions
i.e
, contradiction.
Thus
Thus,
can be
or
. Observing that both of these values work:


Observe


Hence





This means that

Hence


Thus,




Case 1.

This can be easily ruled out by considering the expressions


Case 2.

Firstly, we consider the expressions


If



Since

Consider the expressions


Thus





This post has been edited 8 times. Last edited by SomeonecoolLovesMaths, Mar 6, 2025, 2:58 PM