Show that (a + p)P = a (mod p2), where p is prime, and that, more generally, a = b (mod p) ⇒a= b (mod p²).

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Title: Exploring Congruences in Number Theory**

**Introduction:**

This section delves into a fascinating problem in number theory involving prime numbers and congruences. We aim to demonstrate certain congruence relationships under specified conditions.

**Problem Statement:**

1. **Objective 1:**
   Show that \((a + p)^p \equiv a^p \pmod{p^2}\), where \(p\) is a prime number.

2. **Objective 2:**
   More generally, prove that if \(a \equiv b \pmod{p}\), then \(a^p \equiv b^p \pmod{p^2}\).

**Explanation:**

- The expression \((a + p)^p \equiv a^p \pmod{p^2}\) indicates that raising \(a + p\) to the power of \(p\) results in a number that is congruent to \(a^p\) modulo \(p^2\).

- The general statement involves showing that under the condition \(a \equiv b \pmod{p}\), the p-th powers of \(a\) and \(b\) are equivalent modulo \(p^2\).

**Concepts Involved:**

- **Prime Numbers:** Integers greater than 1 that have no divisors other than 1 and themselves.

- **Modular Arithmetic:** A system of arithmetic for integers, where numbers "wrap around" upon reaching a certain value, the modulus.

- **Congruence:** A relationship that shows two numbers have the same remainder when divided by a certain integer (modulus).

This theory has profound implications in fields such as cryptography and coding theory, where properties of numbers under various operations are essential. Understanding these congruences helps in grasping the fundamental nature of mathematical systems and their applications.
Transcribed Image Text:**Title: Exploring Congruences in Number Theory** **Introduction:** This section delves into a fascinating problem in number theory involving prime numbers and congruences. We aim to demonstrate certain congruence relationships under specified conditions. **Problem Statement:** 1. **Objective 1:** Show that \((a + p)^p \equiv a^p \pmod{p^2}\), where \(p\) is a prime number. 2. **Objective 2:** More generally, prove that if \(a \equiv b \pmod{p}\), then \(a^p \equiv b^p \pmod{p^2}\). **Explanation:** - The expression \((a + p)^p \equiv a^p \pmod{p^2}\) indicates that raising \(a + p\) to the power of \(p\) results in a number that is congruent to \(a^p\) modulo \(p^2\). - The general statement involves showing that under the condition \(a \equiv b \pmod{p}\), the p-th powers of \(a\) and \(b\) are equivalent modulo \(p^2\). **Concepts Involved:** - **Prime Numbers:** Integers greater than 1 that have no divisors other than 1 and themselves. - **Modular Arithmetic:** A system of arithmetic for integers, where numbers "wrap around" upon reaching a certain value, the modulus. - **Congruence:** A relationship that shows two numbers have the same remainder when divided by a certain integer (modulus). This theory has profound implications in fields such as cryptography and coding theory, where properties of numbers under various operations are essential. Understanding these congruences helps in grasping the fundamental nature of mathematical systems and their applications.
Expert Solution
Step 1: Using fermat little theorem

To prove that (a+p)pap(modp2), where p is a prime, it can use binomial expansion and Fermat's Little Theorem. Here's the proof step by step:

1. Fermat's Little Theorem states that if p is a prime number and a is an integer not divisible by p, then ap11(modp). This is a well-known result.

2. Now, it can use Fermat's Little Theorem to simplify (a+p)p:

   (a+p)pap+(p1)ap1p+(p2)ap2p2++pp(modp2)

3. Observe that for every term in this expansion where ap1 appears, it can be replaced by 1 according to Fermat's Little Theorem:

   (a+p)pap+(p1)p+(p2)ap2p2++pp(modp2)

4. Now, it can see that all the terms from (p1)p onward are divisible by p2, so it can eliminate them:

   (a+p)pap+(p1)p(modp2)

5. Since (p1)=p, will have:

   (a+p)pap+p2(modp2)

6. Finally, since p2 is a multiple of p, we can simplify further:

   (a+p)pap(modp2)

This shows that (a+p)pap(modp2) for any integer a and prime p.


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