Euclid’s Theorem, attributed to the ancient Greek mathematician Euclid, establishes that there are infinitely many prime numbers. A prime number is a natural number greater than 1 that is divisible only by 1 and itself.
To illustrate, suppose there are only finitely many primes, listed as p1, p2, …, pn. Consider the number N = (p1 × p2 × … × pn) + 1. This N is not divisible by any of the primes p1 through pn, as dividing N by any pi leaves a remainder of 1. Therefore, N must be either a prime itself or divisible by a prime not in the original list, proving that the list of primes is incomplete and thus infinite.
Table of Contents
- Part 1: OnlineExamMaker AI Quiz Generator – Save Time and Efforts
- Part 2: 20 Euclid’S Theorem Quiz Questions & Answers
- Part 3: AI Question Generator – Automatically Create Questions for Your Next Assessment

Part 1: OnlineExamMaker AI Quiz Generator – Save Time and Efforts
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Part 2: 20 Euclid’S Theorem Quiz Questions & Answers
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1. Question: What does Euclid’s Theorem state?
A. There are infinitely many prime numbers.
B. All prime numbers are odd.
C. There are only finitely many prime numbers.
D. Every even number is prime.
Answer: A
Explanation: Euclid’s Theorem proves that there are infinitely many prime numbers by contradiction, assuming a finite list and showing a contradiction.
2. Question: In Euclid’s proof, what is the key assumption made at the beginning?
A. There are only finitely many primes.
B. All numbers are prime.
C. Primes are evenly distributed.
D. There are no even primes.
Answer: A
Explanation: The proof assumes there are finitely many primes to derive a contradiction, showing that this assumption leads to an impossibility.
3. Question: If you have a list of all primes, say 2 and 3, what number is constructed in Euclid’s proof?
A. (2 × 3) + 1 = 7
B. (2 × 3) – 1 = 5
C. 2 + 3 = 5
D. 2 × 3 = 6
Answer: A
Explanation: The proof constructs N = (product of primes) + 1, which for primes 2 and 3 is 7, and this number is not divisible by 2 or 3.
4. Question: Why is the number constructed in Euclid’s proof not divisible by any prime in the assumed finite list?
A. It leaves a remainder of 1 when divided by them.
B. It is always even.
C. It is a multiple of all primes.
D. It is less than the smallest prime.
Answer: A
Explanation: The constructed number is one more than a multiple of each prime in the list, so it leaves a remainder of 1 and isn’t divisible by them.
5. Question: What happens if the constructed number in Euclid’s proof is prime?
A. It is a new prime not in the list.
B. It contradicts the assumption of finitely many primes.
C. Both A and B.
D. Nothing; it fits the list.
Answer: C
Explanation: If the number is prime, it is not in the original list, contradicting the assumption and proving there are more primes.
6. Question: What happens if the constructed number in Euclid’s proof is composite?
A. It must have a prime factor not in the list.
B. All its factors are in the list.
C. It is equal to one of the primes.
D. It proves there are no primes.
Answer: A
Explanation: If composite, its prime factors cannot all be from the list, as it isn’t divisible by them, so a new prime must exist.
7. Question: Euclid’s Theorem is an example of what type of proof?
A. Proof by contradiction.
B. Direct proof.
C. Inductive proof.
D. Constructive proof.
Answer: A
Explanation: The theorem uses proof by contradiction, assuming the opposite (finitely many primes) and showing it leads to a contradiction.
8. Question: Which of the following is true about the primes generated in Euclid’s proof?
A. They show primes are infinite.
B. They always include 2.
C. They stop at a certain point.
D. They are all even.
Answer: A
Explanation: The process can be repeated indefinitely, demonstrating that no finite list can contain all primes.
9. Question: If we assume the primes are 2, 3, and 5, what is the constructed number?
A. (2 × 3 × 5) + 1 = 31
B. (2 × 3 × 5) – 1 = 29
C. 2 + 3 + 5 = 10
D. 2 × 3 × 5 = 30
Answer: A
Explanation: For primes 2, 3, and 5, the number is 30 + 1 = 31, which is prime and not in the list.
10. Question: Does Euclid’s Theorem apply to all positive integers?
A. Yes, it concerns the infinitude of primes among them.
B. No, it only applies to even numbers.
C. No, it excludes 1.
D. Yes, but only for composites.
Answer: A
Explanation: The theorem addresses primes, which are positive integers greater than 1, proving there are infinitely many.
11. Question: What is the role of the number 1 in Euclid’s Theorem?
A. It is not a prime and doesn’t affect the proof.
B. It is considered a prime in the proof.
C. It is the starting prime.
D. It is used in the construction.
Answer: A
Explanation: 1 is not a prime, so it is excluded from the list, and the proof focuses on primes greater than 1.
12. Question: Can Euclid’s proof be used to find specific primes?
A. Indirectly, by generating new candidates.
B. Yes, it lists all primes.
C. No, it only proves existence.
D. Yes, for even primes only.
Answer: A
Explanation: While it doesn’t list primes, the constructed number can be a new prime, helping to find them.
13. Question: Is there a finite list of primes that Euclid’s Theorem disproves?
A. No, because primes are infinite.
B. Yes, up to a certain number.
C. Yes, all even primes.
D. No, but only for odds.
Answer: A
Explanation: The theorem shows no such finite list exists, as the proof can always produce a new prime.
14. Question: What is a common misconception about Euclid’s Theorem?
A. It claims there are finitely many primes.
B. It only works for small primes.
C. It proves primes are random.
D. Both A and B.
Answer: A
Explanation: Some might think primes are finite, but the theorem directly refutes that.
15. Question: How does Euclid’s Theorem relate to the distribution of primes?
A. It shows primes are unbounded.
B. It gives the exact count of primes.
C. It proves primes are evenly spaced.
D. It limits primes to certain patterns.
Answer: A
Explanation: The theorem establishes that primes continue forever, without bound, in the positive integers.
16. Question: In Euclid’s proof, if the constructed number is divisible by a prime, what must that prime be?
A. Not in the original list.
B. In the original list.
C. Equal to 1.
D. An even number.
Answer: A
Explanation: Any prime factor of the constructed number cannot be from the assumed finite list, proving a new prime.
17. Question: What is the simplest example of Euclid’s proof?
A. Using the prime 2, construct 2 + 1 = 3.
B. Using no primes.
C. Multiplying all odds.
D. Adding primes directly.
Answer: A
Explanation: Starting with 2, the number 3 is prime and not in the list, extending to show infinitude.
18. Question: Does Euclid’s Theorem imply that primes get larger forever?
A. Yes, as there are infinitely many.
B. No, they stop after a point.
C. Yes, but only even ones.
D. No, they repeat.
Answer: A
Explanation: The theorem’s proof shows that larger primes must exist beyond any finite set.
19. Question: What historical significance does Euclid’s Theorem have?
A. It was one of the first proofs of infinitude in mathematics.
B. It ended the study of primes.
C. It was proven by modern computers.
D. It only applies to ancient numbers.
Answer: A
Explanation: Euclid’s work in “Elements” provided early insight into the endless nature of primes.
20. Question: Can Euclid’s Theorem be extended to other number systems?
A. It is specific to positive integers.
B. Yes, to negative numbers.
C. Yes, to fractions.
D. No, it includes irrationals.
Answer: A
Explanation: The theorem applies to the primes in the set of positive integers, as defined in its proof.
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Part 3: AI Question Generator – Automatically Create Questions for Your Next Assessment
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