Is Every Square Integer of the Form 4n or 4n+1?

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Discussion Overview

The discussion revolves around the question of whether the square of any integer can be expressed in the form of 4n or 4n + 1. Participants explore various approaches to proving this concept, including elementary methods and mathematical reasoning.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • Some participants propose that squaring an integer greater than 2 results in a number that is either divisible by four or leaves a remainder of one when divided by four.
  • One participant suggests using base 4 as a hint for the proof.
  • Another participant provides a mathematical expression showing that the square of an even integer (2n) results in 4m, while the square of an odd integer (2n + 1) results in 4k + 1.
  • A participant discusses the concept of finding the next square in a sequence without using the square function, suggesting the formula (n + 1)² = n² + 2n + 1.
  • There is mention of using successor rules to understand how squares progress in modular arithmetic, specifically mod 4.
  • One participant emphasizes the importance of considering different states (even and odd) when proving the claim.
  • Another participant questions the application of the variable "n" in the context of the proof and its validity for integers other than 2.
  • Corrections are made regarding earlier expressions, clarifying the calculations for both even and odd integers.

Areas of Agreement / Disagreement

Participants express various viewpoints and approaches to the problem, but there is no consensus on a single method or proof. The discussion remains open with multiple competing ideas and interpretations.

Contextual Notes

Some participants highlight the need to consider different cases (even vs. odd integers) and the implications of modular arithmetic, but these aspects remain unresolved in the discussion.

DEMJR
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I want to prove that the square of any integer is in the form of 4n or 4n + 1.

I know that when we square any integer greater than 2 the result will be either divisible by four or four divides into the integer and leaves a remainder of one. How would I begin proving this in the most elementary of ways? I just need a boost, not the answer please. Thanks for all your help.
 
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Hi DEMJR! :smile:

Hint: base 4 :wink:
 
(2n)n = 4nn = 4m.
(2n+1)n = 4nn +4n + 1 = 4k + 1.
 
DEMJR said:
I want to prove that the square of any integer is in the form of 4n or 4n + 1.

I know that when we square any integer greater than 2 the result will be either divisible by four or four divides into the integer and leaves a remainder of one. How would I begin proving this in the most elementary of ways? I just need a boost, not the answer please. Thanks for all your help.

If you had a sequence of squares, how could you find the next one? (without using the square function)
 
Mensanator said:
If you had a sequence of squares, how could you find the next one? (without using the square function)
(n+1)2 = n2 + 2n + 1.
 
Good. Now you know that the successor of 0mod4 is 1mod4. Now you just need to find the successor of 1mod4. When you have figured out the successor rules, you just need to find the initial state. Then, with the successor rules in hand, you can build a state machine. As uou already know, not every possible state will appear in the successor rules but the ones that do are good to infinity.
 
DEMJR said:
I want to prove that the square of any integer is in the form of 4n or 4n + 1.

I know that when we square any integer greater than 2 the result will be either divisible by four or four divides into the integer and leaves a remainder of one. How would I begin proving this in the most elementary of ways? I just need a boost, not the answer please. Thanks for all your help.

The answer to most any math problem is to simplify the problem by separately considering every possible state under which the problem can be considered. Working with base 4 as tiny tim suggested requires 4 states for consideration since the units place can be either 0,1,2 or 3. But mathman showed that one need only considered 2 states, either the numbered squared is even (i.e. 2n) or odd (i.e. 2n+1). Mensanator suggests using the successor rule of squares under which the next square state is obtained by adding 2n + 1 to the previous square state where n is the previous number that is squared. It is your choice of what course to take, either one will work.

P.S. do you know how to reduce a number or expression mod 4?, or that (4n + b)^2 = b^2 mod 4?
 
Last edited:
mathman said:
(2n)n = 4nn = ...




(2n+1)n = 4nn +4n + 1 = ...

mathman,

what did you intend to make the chain of thought using the "n' variable?

In each of these, it works for n = 2. But the other positive integers?
 
checkitagain said:
mathman,

what did you intend to make the chain of thought using the "n' variable?

In each of these, it works for n = 2. But the other positive integers?
Typos which I didn't catch. Should be:

(2n)2 = 4n2 = 4m
(2n+1)2 =4n2 + 4n + 1 = 4k + 1
 

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