# Number Theory: Divisibility Proof

• tylerc1991
In summary, Number Theory is a branch of mathematics that studies the properties and relationships of integers, while a Divisibility Proof is a type of mathematical proof that shows if one number is divisible by another without leaving a remainder. To prove divisibility using Number Theory, the fundamental theorem of arithmetic and basic concepts such as prime numbers, factors, and multiples are utilized. Common techniques used in Divisibility Proofs include the division algorithm, Euclid's algorithm, and the principle of mathematical induction. Number Theory and Divisibility Proofs have practical applications in fields such as cryptography, computer science, finance, physics, chemistry, and engineering.
tylerc1991

## Homework Statement

Show that if $p$ is an odd prime of the form $4k + 3$ and $a$ is a positive integer such that $1 < a < p - 1$, then $p$ does not divide $a^2 + 1$

## Homework Equations

If $a$ divides $b$, then there exists an integer $c$ such that $ac = b$.

## The Attempt at a Solution

We have to do this proof by contradiction, so suppose $p$ divides $a^2 + 1$. Then there exists an integer $c$ such that $pc = a^2 + 1$. At this point I am stuck. I can't factor anything, and I don't see any other algebraic manipulations that will help. Any ideas?

## 1. What is Number Theory?

Number Theory is a branch of mathematics that deals with the properties and relationships of integers. It focuses on studying patterns and structures in numbers, as well as their properties and applications.

## 2. What is a Divisibility Proof?

A Divisibility Proof is a type of mathematical proof that shows whether one number is divisible by another number without leaving a remainder. It involves using logical reasoning and mathematical concepts to demonstrate that a certain number is divisible by another number.

## 3. How do you prove divisibility using Number Theory?

To prove divisibility using Number Theory, you need to use the fundamental theorem of arithmetic, which states that every positive integer can be expressed as a unique product of primes. You also need to use basic concepts such as prime numbers, factors, and multiples to demonstrate that a number is divisible by another number.

## 4. What are the common techniques used in Divisibility Proofs?

There are several common techniques used in Divisibility Proofs, including the division algorithm, Euclid's algorithm, and the principle of mathematical induction. These techniques involve breaking down a number into smaller parts and using logical reasoning to demonstrate that it is divisible by another number.

## 5. What are some real-world applications of Number Theory and Divisibility Proofs?

Number Theory and Divisibility Proofs have many practical applications, including in cryptography, computer science, and finance. They are used to develop secure encryption algorithms, optimize computer algorithms, and analyze financial data. Number Theory also has applications in physics, chemistry, and engineering.

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