# Proof by Exhaustion

## Understanding Proof by Exhaustion in Mathematics

Proof by exhaustion is a direct method used to prove a mathematical statement by checking each case individually. This approach does not involve logical arguments and is applicable only when there is a finite number of cases. It is a reliable way to verify a statement by showing that none of the cases disprove it, ultimately leading to the conclusion that the statement is true.

The process of proof by exhaustion involves two main steps: identifying all applicable cases for the statement and proving its truth for each individual case. This means that every case must be demonstrated separately to confirm the statement's validity as a whole. If any case can be disproven, the entire statement is considered false. A deeper understanding of this concept can be gained by exploring the concept of disproof by counterexample.

Let's look at an example to better understand proof by exhaustion. Suppose we want to prove that n²-1 is always a multiple of 3 when n is not a multiple of 3. We can start by establishing the two possible cases: n = 3k + 1 or n = 3k + 2, where k is any integer. Then, we can proceed to prove each case individually, demonstrating that if n = 3k + 1, then n²-1 is a multiple of 3, and similarly for the second case. By satisfying both cases, we can successfully prove the initial statement.

It is essential to note that proof by exhaustion is only suitable when the conjecture can be reduced to a finite number of cases. Attempting to apply this method to an infinite number of cases would be inefficient and never-ending. Hence, it is crucial to consider the size and complexity of the problem before deciding to use proof by exhaustion.

Here are some examples of proofs by exhaustion:

**Example 1:** Proving that p = n² + 2 is not a multiple of 4, where n is an integer and 2≤n≤7.

**Solution:**

Step 1: Split the statement into a finite number of cases.

Given that 2≤n≤7, we can divide the cases into six possibilities: n=2, 3, 4, 5, 6, and 7.

Step 2: Prove that the statement is true for each case.

By substituting each value of n into the given statement and checking if the result is a multiple of 4, we can prove that p is not a multiple of 4 for all of the cases. For example, when n=2, the resulting expression is 6, which is not divisible by 4, and therefore, p is not a multiple of 4. By repeating this process for all the cases, we can conclude that the statement holds true for each individual case, and therefore, the statement as a whole is proven to be true.

**Example 2:** Proving that (p - 1) (p + 1) is a multiple of 12 when p is a prime number between 3 and 25.

**Solution:**

Step 1: Split the statement into a finite number of cases.

For this example, we need to check for each p between 3 and 25 if (p - 1) (p + 1) is a multiple of 12. The prime numbers between 3 and 25 are 5, 7, 11, 13, 17, 19, and 23. So, we can divide the cases into seven possibilities: p=5, 7, 11, 13, 17, 19, and 23.

Step 2: Prove that the statement is true for each case.

We can prove each case separately by substituting the given value of p into the expression and checking if the result is a multiple of 12. By doing so, we can show that (p - 1) (p + 1) is a multiple of 12 for all of the cases, thus proving the statement to be true for each individual case.

In conclusion, proof by exhaustion is a valuable method in mathematics that allows us to prove statements with finite cases. By following a simple two-step process, we can systematically prove that a statement is true by exhausting all the possible cases.

## The Importance of Proof by Exhaustion in Mathematics

Proof by exhaustion is a valuable method in mathematics that allows us to prove the validity of a statement or theorem when there are only a limited number of cases to consider. This approach involves systematically testing each case and showing that it holds true, thus proving the statement to be true for all cases.

### Understanding the Process of Proof by Exhaustion

To utilize proof by exhaustion, it is crucial to first identify all the potential cases that need to be examined. This requires a thorough understanding of the statement or theorem being proven.

Next, the proof is carried out by individually testing each case. This may involve performing calculations, making logical deductions, or using other means of proof. The goal is to demonstrate that every case holds true, proving the statement's overall validity.

If all cases are found to be true, the proof is considered complete, and the statement is proven to be true. However, if even one case does not hold true, the statement as a whole is disproved.

### The Significance of Proof by Exhaustion

Proof by exhaustion is necessary in mathematics as it allows us to systematically and conclusively prove statements or theorems with a limited number of cases. This method ensures the accuracy and reliability of mathematical proofs, providing a solid foundation for further study and application.

## The Significance of Proof by Exhaustion in Mathematics

In the world of mathematics, proof by exhaustion plays a critical role in proving statements that may not have a general solution. This method breaks down a statement into specific cases and uses numerical or logical methods to prove it in a finite number of steps.

The application of proof by exhaustion also comes in handy for difficult-to-prove statements, offering a systematic and clear approach that leaves no room for doubt.

## Is Proof by Exhaustion a Form of Direct Proof?

Indeed, proof by exhaustion is considered a type of direct proof. Direct proofs involve working through a statement logically, starting from known facts or assumptions and utilizing logical steps to demonstrate its truth.

When using proof by exhaustion, we use established facts or assumptions to test each individual case and establish its truth. In doing so, we achieve a direct proof of the statement for all cases.

## The Crucial Role of Exhaustively Testing All Cases

The term "exhaustion" in proof by exhaustion emphasizes the significance of considering and testing all potential cases. This method relies on thoroughness and eliminates any possibility for assumptions or shortcuts. By exhaustively testing each case, we can confidently establish the truth of the statement.

## In Conclusion

To summarize, proof by exhaustion is a powerful tool in mathematics, enabling us to prove statements by examining each case individually. This method requires meticulous analysis and avoids any shortcuts, making it a dependable and comprehensive approach for proving statements. Understanding and utilizing proof by exhaustion can greatly benefit one's approach to mathematical proofs.