Understanding Modular Arithmetic: Exploring Congruence Modulo 5

  • Thread starter TheMathNoob
  • Start date
In summary, congruence mod n means that two numbers have the same remainder when divided by n. In the case of n congruent to 6 mod 5, n is also congruent to 1 mod 5 because 5 divides n-6, and when divided by 5, the remainder is 1. However, in the case of 16 congruent to 2 mod 7, even though 7 divides 16-2, the remainder when dividing by 7 is not 2. Therefore, it is not necessary for b to be a perfect square in order for a^2 to be congruent to b mod n.
  • #1
TheMathNoob
189
4

Homework Statement


if n is congruent to 6 mod 5
then n is congruent to 1 mod 5?

Homework Equations

The Attempt at a Solution


[/B]
This is not a problem. It's a doubt that I have
 
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  • #2
TheMathNoob said:

Homework Statement


if n is congruent to 6 mod 5
then n is congruent to 1 mod 5?

Homework Equations

The Attempt at a Solution


[/B]
This is not a problem. It's a doubt that I have
Can you write 6 as congruent to x mod 5? What is x?
 
  • #3
ehild said:
Can you write 6 as congruent to x mod 5? What is x?
x is a number between 0 and 5
 
  • #4
What does it mean that a number n is congruent to x mod 5?
 
  • #5
ehild said:
What does it mean that a number n is congruent to x mod 5?
5 divides n-x
 
  • #6
TheMathNoob said:
5 divides n-x
Yes, but you said that x must be between 0 and 5. Which number is x if n=6?
 
  • #7
TheMathNoob said:
5 divides n-x
ehild said:
Yes, but you said that x must be between 0 and 5. Which number is x if n=6?
I got it by algebra 5 divides n-6 so n-6=5k, n=5(k+1)+1, so 5 divides n-1 which implies n is congruent to 1 mod 5. I am having another inquiry with my friend. He claims that 16 is not congruent to 2 mod 7 because he thinks that a^2 congruent to b mod n implies that b has to be a perfect square. Is that correct?
 
  • #8
TheMathNoob said:
I got it by algebra 5 divides n-6 so n-6=5k, n=5(k+1)+1, so 5 divides n-1 which implies n is congruent to 1 mod 5.
Correct.
TheMathNoob said:
I am having another inquiry with my friend. He claims that 16 is not congruent to 2 mod 7 because he thinks that a^2 congruent to b mod n implies that b has to be a perfect square. Is that correct?

a congruent to b mod n implies that a=kn+b. It follows that a2=(kn+b)2=k2n2+2knb+b2. If you divide that by n, the remainder is b2. But that remainder can be greater than n. It is the case with your example. 16 = 42, and 4 is 4 mod 7, so k=0, and b2=16. You have to do the division further to get 16 = 2*7+2. 16 is congruent to 2 mod 7.
 

What is modular arithmetic?

Modular arithmetic is a branch of mathematics that deals with the remainder after dividing two numbers. It is often used in cryptography and computer science to solve problems involving repeating patterns or cycles.

What is congruence modulo 5?

Congruence modulo 5 is a specific type of modular arithmetic where the numbers are divided by 5 and the remainder is considered. Two numbers are said to be congruent modulo 5 if they have the same remainder when divided by 5.

How is modular arithmetic used?

Modular arithmetic is used in various fields such as computer science, cryptography, and number theory. It is often used to solve problems involving repeating patterns or cycles, in encryption algorithms, and in identifying patterns in data.

What are some applications of congruence modulo 5?

Congruence modulo 5 has various applications in real-world problems. It is used in clock arithmetic, where the numbers on a clock repeat every 12 hours or 24 hours. It is also used in music theory to identify repeating patterns and in coding theory to detect errors in transmitted data.

How is congruence modulo 5 different from regular arithmetic?

In regular arithmetic, the quotient and remainder are both considered when dividing two numbers. In congruence modulo 5, only the remainder is considered. This means that numbers that are normally considered different in regular arithmetic can be considered congruent modulo 5. For example, 22 and 17 are not equal in regular arithmetic, but they are congruent modulo 5 because they both have a remainder of 2 when divided by 5.

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