New Year's Math Problem
=======================
Toards the end of the year 2023 and the beginning of 2024, I found
a math puzzle on Quora[1]. Don't worry, those puzzles are pretty easy.
If solutionns exists, then the numbers are small.
The question is if there exists integers x,y, such that:
x²⁰²⁴-y²⁰²⁴=2025²⁰²⁵
The first step is to check which of the variables is odd and which is
even.
You can find easily that x is odd and y is even.
Now, let us find a number easy to deal with, call it 'a', such that
2025≢1 mod a
or
a∤2024
Guss what? 16 is such a number. And 2025≡9 mod 16
Now, 2024 is a multiple of 4. And if a number 'a' is odd it can be represented
as
4n±1
and
(4n±1)⁴=(4n)⁴±4(4n)³+6(4n)³±4(4n)+1=
=256n⁴±256n³+96n³±16n+1=
=16(16n⁴±16n³+6n³±n)+1≡1 mod 16==>
==> x²⁰²⁴≡1 mod 16 ==>
==> x²⁰²⁴-y²⁰²⁴≡1 mod 16
while
2025²⁰²⁵=2025⋅2025²⁰²⁴≡9 mod 16
There are no real solutions.
[1]
https://qr.ae/pKcDdK