Sum of Two Squares: Is There a Relation?

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Discussion Overview

The discussion revolves around the mathematical properties and relationships of numbers that can be expressed as the sum of two squares. Participants explore potential connections between pairs of numbers that satisfy this condition, particularly focusing on even numbers and their representations in terms of other numbers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether there are relations between pairs of numbers (a, b) and (m, n) beyond the equality a² + b² = m² + n².
  • Another participant suggests a relation involving the differences of squares: a² - m² = n² - b², leading to the factorization (a - m)(a + m) = (n - b)(n + b).
  • Further relations are proposed, including a² - n² = m² - b² and additional factorization forms involving (a - n)(a + n) and (m - b)(m + b).
  • A participant introduces a theorem regarding primes of the form 1 (mod 4) and their unique representation as sums of two squares, along with conditions for even numbers to be expressed as such.
  • It is noted that an even number can be expressed as a sum of two squares in multiple ways depending on its prime factorization, particularly when involving primes of the form 1 (mod 4) and certain conditions related to primes of the form 3 (mod 4).

Areas of Agreement / Disagreement

Participants present various mathematical relationships and properties, but there is no consensus on a singular relation between (a, b) and (m, n) beyond the established equality. The discussion includes multiple competing views and interpretations of the conditions under which numbers can be expressed as sums of two squares.

Contextual Notes

Some mathematical claims depend on specific conditions related to the forms of primes and their representations, which may not be universally applicable without further clarification or assumptions.

smslca
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sum of two squares?

If an Even number could be expressed in the form a2 + b2 . And if there exits two other numbers m,n such that
a2 + b2 = m2 + n2

then , my question is

is there any relation between (a,b) and (m,n) apart from a2 + b2 = m2 + n2 ??
 
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Well, there is the obvious a^2- m^2= n^2- b^2 so that (a- m)(a+ m)= (n- b)(n+ b).
 


HallsofIvy said:
Well, there is the obvious a^2- m^2= n^2- b^2 so that (a- m)(a+ m)= (n- b)(n+ b).

Or, there is a^2- n^2= m^2- b^2.
 


HallsofIvy said:
Well, there is the obvious a^2- m^2= n^2- b^2 so that (a- m)(a+ m)= (n- b)(n+ b).

configure said:
Or, there is a^2- n^2= m^2- b^2.

So other relations between (a,b) and (m,n) include

(a-m)(a+m) = (n-b)(n+b)

(a-n)(a+n) = (m-b)(m+b)

All of the numbers must solve both of these equations.
 


A prime of form 1 (mod 4) can be uniquely written as sum of two squares.

An even number can be uniquely expressed as a sum of two squares if it is twice a prime of form 1 (mod 4). (or if it is multiplied with any square of number of form 3 (mod 4)).

A number which is product of N distinct primes of form 1 (mod 4) can be represented as sum of two squares in N different ways.
Thus, an even number can be written as sum of two squares in N different ways if it is twice that value (or product of that with any square of number that is equivalent to form 3 (mod 4)).

For more information, please see
refer to this thread.
http://mersenneforum.org/showthread.php?t=13027
 

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