Proving gcd(r,s)=1 with gcd(r^2-s^2, r^2+s^2)

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In summary, the conversation discusses proving that if gcd(r,s)=1, then gcd(r^2-s^2, r^2+s^2)=1 or 2. The person is initially confused but then understands the proof provided by another person in the conversation.
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awesome220
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Can anyone help me with this?

If gcd(r,s)=1 then prove that gcd(r^2-s^2, r^2+s^2)=1 or 2.

i'm so confused.
 
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  • #2
awesome220 said:
Can anyone help me with this?

If gcd(r,s)=1 then prove that gcd(r^2-s^2, r^2+s^2)=1 or 2.

i'm so confused.

Suppose [itex]n|(r^2-s^2)[/itex] and [itex]n|(r^2+s^2)[/itex]. (This would be the case for the gcd of the two expressions.) Then there are some integers a, b with
[tex]an=r^2-s^2[/tex] and [tex]bn=r^2+s^2[/tex].
Then [itex](a+b)n=2r^2[/itex] and so n divides [itex]2r^2[/itex]. Does this help?
 
  • #3
I understand, but how does that give us that gcd (r^2-s^2, r^2+s^2) = 1 or 2?
 
  • #4
nevermind, I think i see it! Thanks!
 

Related to Proving gcd(r,s)=1 with gcd(r^2-s^2, r^2+s^2)

What is GCD (Greatest Common Divisor)?

GCD (Greatest Common Divisor) is the largest positive integer that divides two or more numbers without leaving any remainder.

How is GCD calculated?

There are several methods for calculating GCD, including using prime factorization, Euclid's algorithm, or using a GCD calculator. The most commonly used method is Euclid's algorithm, which involves finding the remainder of the larger number divided by the smaller number, and then repeating the process with the smaller number and the remainder until the remainder is equal to 0. The last non-zero remainder is the GCD.

What is the significance of GCD in mathematics?

GCD is an important concept in number theory and is commonly used in various mathematical calculations, including simplifying fractions, finding equivalent fractions, and reducing algebraic expressions. It is also used in cryptography and coding theory.

Can GCD be negative?

No, GCD is always a positive integer. This is because it represents the largest positive number that can divide two or more given numbers without leaving a remainder.

How is GCD used in real-life situations?

GCD is used in various real-life situations, such as simplifying recipes, dividing items into equal groups, and finding the lowest common denominator in fractions. It is also used in computer science, such as in the implementation of algorithms and data structures.

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