Mathematical Counterexamples Quiz

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Questions and Answers

What concept is tested in TMUA 2021 related to integers?

  • Functions
  • Factors of Integers (correct)
  • Rational Numbers
  • Irrational Numbers

Which TMUA exam year features prime numbers as a topic?

  • TMUA 2022 and TMUA 2021 (correct)
  • TMUA 2023 only
  • TMUA 2021 and TMUA 2023
  • TMUA 2022 only

Which of the following was a focus in both TMUA 2021 assessments?

  • Counterexamples (correct)
  • Sequences and Series
  • Probability Theory
  • Polar Coordinates

What type of statements are examined in TMUA 2023 regarding mathematical expressions?

<p>Statements with Exponents (B)</p> Signup and view all the answers

Which content area was deemed medium difficulty across two different TMUA years?

<p>Counterexamples (A)</p> Signup and view all the answers

Flashcards

Counterexample (TMUA 2023)

An example that proves a statement is false.

Counterexample (TMUA 2022)

A specific case that shows a statement is incorrect.

Counterexample (TMUA 2021)

Example showing a statement is NOT always true.

Counterexample (TMUA 2021)

Example that disproves a mathematical statement.

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Prime Numbers

Whole numbers greater than 1, divisible only by 1 and themselves.

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Factors of Integers

Whole numbers that divide evenly into another number.

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Statements with Exponents

Mathematical expressions using exponents.

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Study Notes

Counterexamples: Statements with Exponents

  • Claim: For all positive real numbers x and y, √x = x√y
  • Counterexample I: x = 1, y = 16. √1 = 1 and 1√16 = 1*4 = 4. This is not a counterexample as it does not satisfy the claim.
  • Counterexample II: x = 2, y = 8. √2 ≠ 2√8 = 2*2√2. This is a counterexample.
  • Counterexample III: x = 3, y = 4. √3 ≠ 3√4 = 3*2=6. This is not a counterexample.
  • Correct Answer: II only

Counterexamples: Prime Numbers

  • Claim: If n is prime, then n² + 2 is not prime.
  • Counterexample I: n = 2. 2² + 2 = 6, which is not prime. This is not a counterexample, as the claim is satisfied.
  • Counterexample II: n = 3. 3² + 2 = 11, which is prime. This is a counterexample.
  • Counterexample III: n = 4. 4² + 2 = 18. This is not prime. Not a counterexample.
  • Correct Answer: II only

Counterexamples: Factors of Integers

  • Claim: If a is a factor of bc, then a is a factor of b or a is a factor of c.
  • Counterexample I: a = 5, b = 10, c = 20. 5 is a factor of 10*20, and 5 is a factor of 10, so this is not a counterexample.
  • Counterexample II: a = 8, b = 4, c = 4. 8 is a factor of 4*4. 8 is not a factor of 4. This is a counterexample.
  • Counterexample III: a = 6, b = 7, c = 12. 6 is a factor of 7*12 = 84, and 6 is a factor of 12, so this is not a counterexample.
  • Correct Answer: II only

Counterexamples: Sequence of Positive Integers

  • Sequence: u₁ = 15, u₂ = 21, u₃ = 30, u₄ = 37, u₅ = 44, u₆ = 51, u₇ = 59
  • Claim: If n is a prime number, then uₙ is a multiple of 3 or uₙ is a multiple of 5.
  • Counterexample: n = 5. u₅ = 44 is not a multiple of 3 or 5. This is the smallest counterexample.
  • Correct Answer: 5

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