Problem 7 - Discrete Mathematics with Applications

Question

Prove each directly. The square of an even integer is even.

Step-by-Step Solution

Answer

In order to prove that the square of an even integer is even, we can follow these steps: 1. Define an even integer as \(k = 2n\), where \(n\) and \(k\) are integers. 2. Square the even integer: \(k^2 = (2n)^2\). 3. Simplify the expression: \(k^2 = 4 \cdot n^2\). 4. Since the result is an integer, \(n^2\), multiplied by 4 (which is a multiple of 2), it shows that \(k^2\) is an even integer. Therefore, we have proven that the square of an even integer is even.

Step 1: Define Even Integer

An integer is even if it can be expressed as 2 times another integer. In other words, let's call the integer \(n\), then the even integer can be defined as \(k = 2n\), where \(n\) and \(k\) are integers.

Step 2: Square the Even Integer

Now, we want to prove that the square of an even integer is also even. Let's square the even integer \(k\): \[k^2 = (2n)^2\]

Step 3: Simplify the Expression

Next, we will simplify the expression by applying the exponent rules: \[k^2 = (2n)^2 = 2^2 \cdot n^2 = 4 \cdot n^2\]

Step 4: Show the Result Is Even

The result we obtained in step 3 is \(4 \cdot n^2\). By the definition of even integers, any integer multiplied by 2 is an even integer. In our result, we have an integer \(n^2\) multiplied by 4, which is a multiple of 2 (remember that \(n\) and \(k\) are integers, and therefore \(n^2\) is an integer too). Therefore, \(k^2\) is an even integer. In conclusion, we have proven that the square of an even integer is even.

Key Concepts

Properties of Integers

Understanding the properties of integers is essential in the foundational study of mathematics. Integers are whole numbers that include zero, positive, and negative numbers without any fractional or decimal part. These numbers possess several interesting properties:

• Closure Property: The sum or product of any two integers will always result in another integer, showing closure under addition and multiplication.
• Commutative Property: The order of addition or multiplication doesn't affect the outcome, meaning for any integers, say \(a\) and \(b\), \(a+b = b+a\) and \(a\times b = b\times a\).
• Associative Property: When adding or multiplying, the way numbers are grouped doesn't change their sum or product, such as \((a+b) + c = a + (b+c)\) and \((a\times b) \times c = a\times (b\times c)\).
• Distributive Property: This connects addition with multiplication, for example, \(a(b+c) = ab + ac\).

Identifying even and odd integers is also important; an even integer is a number that can be exactly divided by 2, such as 2, 4, and 6, while an odd integer leaves a remainder of 1 when divided by 2. These properties are helpful in proving various mathematical hypotheses and theorems.

Integer Square

When you square an integer, it means multiplying the integer by itself. This can have some interesting results. Specifically, when dealing with even integers, there is a fundamental property: squaring an even integer results in another even integer. Let’s explore this further:
Suppose we have an even integer defined as \(k = 2n\), where both \(k\) and \(n\) are integers. If we square \(k\), we calculate:

• \(k^2 = (2n)^2 = 4n^2\)

Here, the expression \(4n^2\) indicates that the square is a multiple of 4, which implies it's also a multiple of 2, and thus another even integer. This demonstration is crucial in illustrating the nature of integer squares.
Further, the concept of squaring helps in identifying patterns and solving equations, as squaring preserves the parity (evenness or oddness) of the original integer.

Mathematical Proof

A mathematical proof is a logical argument that verifies the truth of a mathematical statement. Proofs are essential to establish confidence in mathematical formulae and results. They combine clear reasoning with mathematical properties.
One common style of proof is direct proof. It starts with known truths and uses logical steps to arrive at the statement to be proven. For example, proving that the square of an even integer is even involves:

• Defining the statement clearly, i.e., starting with \(k = 2n\) for an even integer.
• Squaring the integer, leading to \(k^2 = 4n^2\).
• Recognizing from properties of integers that \(4n^2\), twice a multiple of 2, results in an even integer.

Proofs may seem complex, but they follow a systematic approach. Each step is based on established mathematical rules and properties, offering irrefutable conclusions. They are the backbone of validating every mathematical theory or conjecture, ensuring that results are both reliable and reproducible.